The synthesis of a series of CgPAr ligands is reported, where CgP is the 6-phospha-2,4,8-trioxa-1,3,5,7-tetramethyladamant-6-yl moiety and Ar = 2-pyridyl (L2), 3-pyridyl (L3), 2-pyrimidyl (L4), 4-R-2-pyridyl [R = Me (L5a), CF3 (L6a), SiMe3 (L7a)] or 6-R-2-pyridyl [R = Me (L5b), CF3 (L6b), SiMe3 (L7b). Testing of these ligands in the Pd-catalysed methoxycarbonylation of phenylacetylene reveals that the activity and branched selectivity of the catalysts derived from these ligands varies as a function of the N-heterocycle, with the catalyst derived from L5b being the most active of those tested. This, together with the poor performance of catalysts derived from L3 supports the hypothesis that the catalysis proceeds by a “proton shuttling” mechanism, an idea that previously had only been applied to arylphosphines. Reaction of [PtCl2(cod)] with L where L = L2 or L4–7 yields a rac/meso mixture of the trans-[PtCl2(L)2] (1a–h) complexes, three of which are structurally characterised. 31P NMR spectroscopy shows that reaction of L3 with [PtCl2(cod)] gives a mixture of mononuclear and binuclear metal complexes in solution. The complex trans-[PdCl2(L2)2] (4) reacts with AgBF4 to give the [PdCl(κ1-L2)(κ2-L2)]BF4 (5) with spectroscopic and structural characterisation confirming the presence of a P,N-chelate. 1H and 31P NMR evidence supports the assignment of a pyridyl-protonated species being formed upon treatment of 4 with TsOH·H2O in CD2Cl2; both the protonated species and chelate 5 are observed when the reaction is carried out in MeOH.

9-Amino-9-phosphabicyclo[3.3.1]nonanes, (PhobPNHR′; R = Me or iPr) are readily prepared by aminolysis of PhobPCl and are significantly less susceptible to hydrolysis than the acyclic analogues Cy2PNHR′. Treatment of Cy2PNHMe with Cy2PCl readily gave Cy2PNMePCy2. By contrast, treatment of PhobPCl with PhobPNHMe in the presence of Et3N does not afford PhobPNMePPhob but instead the salt [PhobP(NMeH)PPhob]Cl is formed which, upon addition of [PtCl2(NCtBu)2] gives the zwitterionic complex [PtCl3(PhobP(NMeH)PPhob)]. The neutral PhobP(NMe)PPhob is accessible from PhobNMeLi and is converted to the chelate [PdCl2(PhobPNMePPhob)] by addition of [PdCl2(cod)]. The anomalous preference of the PhobP group for the formation of PPN products is discussed. The unsymmetrical diphos ligands PhobPNMePAr2 (Ar = Ph, o-Tol) are prepared, converted to [Cr(CO)4(PhobPNMePAr2)] and shown to form Cr-catalysts for ethene oligomerisation, producing a pattern of higher alkenes that corresponds to a Schulz-Flory distribution overlaid on selective tri/tetramerisation.

A chlorosilane elimination reaction has been developed that allows the efficient synthesis of optically pure C1-symmetric, C1-backboned diphosphines with a wide variety of stereoelectronic characteristics.

Substantially more active iron catalysts for a standard Negishi cross-coupling are obtained when bis(diarylphosphino)thiophenes are employed in place of the benchmark ligand bis(diphenylphosphino)benzene. The thiophene ligands have the advantages of ease of synthesis and ready modification.

Azaborinylphosphines are readily prepared by the reaction of silylphosphines with a chloroborane under mild conditions; they are shown to contain P–B bonds that are sufficiently robust to allow these ligands to be used in homogeneous catalysis.

Diazaborinylphosphines based on the 1,8-diaminonaphthylboronamide heterocycle are prepared by a chlorosilane-elimination reaction, and their structural and bonding properties are compared to those of PPh3. The precursor chloroborane ClB{1,8-(NH)2C10H6} (I) is fully characterized including its crystal structure, which features intermolecular π–π stacking, B···N interactions, and N–H···Cl hydrogen bonding. Treatment of I with Ph3–nP(SiMe3)n gave the corresponding Ph3–nP(B{1,8-(NH)2C10H6})n, {L1 (n = 1), L2 (n = 2), and L3 (n = 3)}. The crystal structures of L1–3 reveal an increase in the planarity at P as a function of n, and the steric bulk of the diazaborinyl substituent B{1,8-(NH)2C10H6} is similar to that of a phenyl. Nucleus-independent chemical shift calculations were carried out that suggest that the 14 π-electron diazaborinyl substituent can be described as aromatic overall, though the BN2-containing ring is slightly antiaromatic. The complexes cis-[Mo(L1–3)2(CO)4] (1–3) are prepared from [Mo(nbd)(CO)4] (nbd = norbornadiene) and L1–3. From the position of the ν(CO) (A1) band in the IR spectra of 1–3, it is deduced that the diazaborinyl substituent has a donating capacity similar to an alkyl group.

Correction for ‘Reversible CO exchange at platinum(0). An example of similar complex properties produced by ligands with very different stereoelectronic characteristics’ by Sebastian J. K. Forrest et al., Dalton Trans., 2014, DOI: 10.1039/c4dt02303j.

The cobalt PCP pincer complexes [Co{2,6-(CH2PPh2-κP)2C6H3-κC1}(L)2], where L = PMe3 (1), CO (2), have been prepared. Complex 1 is obtained by a transmetalation reaction between 1-lithio-2,6-bis((diphenylphosphino)methyl)benzene and [CoCl(PMe3)3]. Subsequent exposure of 1 to CO gave complex 2. Complexes 1 and 2 can also be obtained from 1,3-bis((diphenylphosphino)methyl)benzene and [CoMe(PMe3)4]. Instead of ortho metalation occurring directly at the C2 (pincer) position of the diphosphine, ortho metalation first occurs at the C4 position to form [Co{2-(CH2PPh2-κP)-4-(CH2PPh2)-C6H3-κC1}(PMe3)3] (4). After reflux of the reaction mixture for 24 h, a rearrangement of 4 occurs to give pincer complex 1 with loss of PMe3 in ca. 50% yield; this rearrangement was accompanied by some decomposition. The mechanism for the conversion of 4 to 1 has been probed using 1-deuterio-2,6-bis((diphenylphosphino)methyl)benzene. Unexpectedly, the labeled ligand led to 15% deuterium enrichment of an ortho CH of the terminal PPh2 group in the product complex 1, and the proposed mechanism for this rearrangement involves a four-membered cobaltacyclic intermediate.

The four isomers of 9-butylphosphabicyclo[3.3.1]nonane, s-PhobPBu, where Bu = n-butyl, sec-butyl, isobutyl, tert-butyl, have been prepared. Seven isomers of 9-butylphosphabicyclo[4.2.1]nonane (a5-PhobPBu, where Bu = n-butyl, sec-butyl, isobutyl, tert-butyl; a7-PhobPBu, where Bu = n-butyl, isobutyl, tert-butyl) have been identified in solution; isomerically pure a5-PhobPBu and a7-PhobPBu, where Bu = n-butyl, isobutyl, have been isolated. The σ-donor properties of the PhobPBu ligands have been compared using the JPSe values for the PhobP(═Se)Bu derivatives. The following complexes have been prepared: trans-[PtCl2(s-PhobPR)2] (R = nBu (1a), iBu (1b), sBu (1c), tBu (1d)); trans-[PtCl2(a5-PhobPR)2] (R = nBu (2a), iBu (2b)); trans-[PtCl2(a7-PhobPR)2] (R = nBu (3a), iBu (3b)); trans-[PdCl2(s-PhobPR)2] (R = nBu (4a), iBu (4b)); trans-[PdCl2(a5-PhobPR)2] (R = nBu (5a), iBu (5b)); trans-[PdCl2(a7-PhobPR)2] (R = nBu (6a), iBu (6b)). The crystal structures of 1a–4a and 1b–6b have been determined, and of the ten structures, eight show an anti conformation with respect to the position of the ligand R groups and two show a syn conformation. Solution variable-temperature 31P NMR studies reveal that all of the Pt and Pd complexes are fluxional on the NMR time scale. In each case, two species are present (assigned to be the syn and anti conformers) which interconvert with kinetic barriers in the range 9 to >19 kcal mol–1. The observed trend is that, the greater the bulk, the higher the barrier. The magnitudes of the barriers to M–P bond rotation for the PhobPR complexes are of the same order as those previously reported for tBu2PR complexes. Rotational profiles have been calculated for the model anionic complexes [PhobPR-PdCl3]− using DFT, and these faithfully reproduce the trends seen in the NMR studies of trans-[MCl2(PhobPR)2]. Rotational profiles have also been calculated for [tBu2PR-PdCl3]−, and these show that the greater the bulk of the R group, the lower the rotational barrier: i.e., the opposite of the trend for [PhobPR-PdCl3]−. Calculated structures for the species at the maxima and minima in the M–P rotation energy curves indicate the origin of the restricted rotation. In the case of the PhobPR complexes, it is the rigidity of the bicycle that enforces unfavorable H···Cl clashes involving the Pd–Cl groups with H atoms on the α- or β-carbon in the R substituent and H atoms in 1,3-axial sites within the phosphabicycle.

The reaction of tetrasulfonated calix[4]arene (trioctylammonium salt) with P(NMe2)3 followed by treatment with gaseous NMe2H gave a zwitterionic six-coordinate phosphorus(V) species 1 containing a P(H)(NHMe2) group which can be stored for months without decomposition. In water, 1 loses NHMe2 and rearranges to form the water soluble phosphite Lcc. Phosphite Lcc has a half-life in water of ca. 5 h decomposing to H3PO3 and free tetrasulfonated calix[4]arene. Compound 1 serves as a convenient precursor to Lcc and complexes of Lcc are formed by dissolving 1 in water in the presence of labile metal complexes. The products have been identified by comparison of their 31P NMR data with well established analogues of calix[4]arene derived phosphites. In this way the water soluble complexes [Rh(acac)(CO)(Lcc)2] (2c) [Rh2Cl2(CO)2(Lcc)2] (3c), [Pt2Cl4(Lcc)2] (4c) and [PtCl2(Lcc)2] have been tentatively identified. The rhodium complex 3c has a half-life in water of 4 months. Two-phase (water/toluene) hydroformylation of 2-methylpentenoate with 2c as a catalyst has been investigated and the results compared with the same reaction in toluene with lipophilic analogues of 2c. Under mild conditions, with 2ccatalyst, branched aldehydes are the only products of hydroformylation and one of the branched aldehydes is selectively hydrogenated to give the lactone derivative.

The homodiphosphanes CgP–PCg (1) and PhobP–PPhob (2) and the heterodiphosphanes CgP–PPhob (3), CgP–PPh2 (4a), CgP–P(o-Tol)2 (4b), CgP–PCy2 (4c), CgP–PtBu2 (4d), PhobP–PPh2 (5a), PhobP–P(o-Tol)2 (5b), PhobP–PCy2 (5c), PhobP–PtBu2 (5d) where CgP = 6-phospha-2,4,8-trioxa-1,3,5,7-tetramethyladamant-9-yl and PhobP = 9-phosphabicyclo[3.3.1]nonan-9-yl have been prepared from CgP(BH3)Li or PhobP(BH3)Li and the appropriate halophosphine. The formation of 1 is remarkably diastereoselective, with the major isomer (97% of the product) assigned to rac-1. Restricted rotation about the P–P bond of the bulky meso-1 is detected by variable temperature 31P NMR spectroscopy. Diphosphane 3 reacts with BH3 to give a mixture of CgP(BH3)–PPhob and CgP–PPhob(BH3) which was unexpected in view of the predicted much greater electron-richness of the PhobP site. Each of the diphosphanes was treated with dimethylacetylene dicarboxylate (DMAD) in order to determine their propensity for diphosphination. The homodiphosphanes 1 and 2 did not react with DMAD. The CgP-containing heterodiphosphanes 4a–d all added to DMAD to generate the corresponding cisalkenes CgPCH(CO2Me)CH(CO2Me)PR2 (6a–d) which have been used in situ to form chelate complexes of the type [MCl2(diphos)] (7a–d) where M = Pd or Pt. The PhobP-containing heterodiphosphanes 3 and 5a–d react anomalously with DMAD and do not give the products of diphosphination. The X-ray crystal structures of the diphosphanes 2, 3, 4a, and 5a, the monoxide and dioxide of diphosphane 1, and the platinum chelate complex 7c have been determined and their structures are discussed.

The cage monophosphinites CgPOR {where CgP = 6-phospha-2,4,8-trioxa-adamantane and R = C6H5 (La); 2-C6H4CH3 (Lb); 2,4,6-C6H2(CH3)3 (Lc); 2,4-C6H3tBu2 (Ld); CH3 (Le); CH2CF3 (Lf)} and diphosphinites CgPZPCg {where ZH2 = 2,2′-biphenol (Lg) or 1,2-benzenedimethanol (Lh)} have been made from CgPBr and the corresponding alcohol or phenol. The cage phosphinites are remarkably stable to water. All the ligands La−h have been tested for nickel(0)-catalyzed hydrocyanation of 3-pentenenitrile in the presence of Lewis acids (ZnCl2, Ph2BOBPh2, or iBu2AlOAliBu2), and tentative structure−activity relationships are suggested. The hydrocyanation activities obtained with catalysts derived from monophosphinite Lf (with iBu2AlOAliBu2) and diphosphinite Lh (with ZnCl2) are comparable with the commercial catalyst based on P(OTol)3. The complexes trans-[PtCl2(L)2] where L = La (1a), Le (1e), and Lf (1f) and the chelate cis-[PtCl2(Lh)] (1h) are reported. From the νCO values for the complexes trans-[RhCl(CO)(La−f)2] (2a−f), it is concluded that ligand Lf is the most phosphite-like of the monophosphinites. Treatment of [Ni(cod)2] (cod = 1,5-cyclo-octadiene) with Lh leads to a mixture of products, one of which was characterized as the binuclear [Ni2(Lh)2(μ-cod)] (3h). The crystal structures of Lh, 1a, 1e, 1f, 1h·2CH2Cl2, and 3h·3C6H5CH3 are reported.

An efficient, classical resolution of the versatile P-ligand intermediate 6-phospha-2,4,8-trioxa-adamantane (CgPH) is described and the rhodium complex of the optically pure secondary phosphine β-CgPH is an active and moderately selective asymmetric hydrogenation catalyst.

The enantioselective hydrogenation catalyst [Rh(α-CgPH)2(cod)]BF4, (CgPH = 6-phospha-2,4,8-trioxa-adamantane) exists in solution as a mixture of two slowly interconverting rotamers, one with C2- and the other with C1-symmetry.

The homologous series of diphosphines (CH2)n−1P(CH2)3P(CH2)n−1 where n = 5 (L5), 6 (L6), or 7 (L7) have been synthesized from the corresponding PhP(CH2)n−1. Treatment of [PtCl2(cod)] with L5–7 gave the 6-membered chelates cis-[PtCl2(L5–7)], the crystal structures for which reveal that L5–7 have very similar steric bulk and bite angles. Treatment of [Rh2Cl2(CO)4] with L5–7 gave the binuclear trans-[Rh2Cl2(CO)2(μ-L5–7)2] with syn and anti orientations of the CO and Cl ligands suggested by the 31P NMR spectra and the crystal structures of syn–trans-[Rh2Cl2(CO)2(μ-L5)2] and anti–trans-[Rh2Cl2(CO)2(μ-L7)2]. The ν(CO) values for trans-[Rh2Cl2(CO)2(μ-L5–7)2] indicate that the donor strength increases in the order L5 < L6 < L7. A study of rhodium-catalysed hydroformylation of 1-octene using diphosphines L5–7 is described. The catalyst activity decreases with increasing phosphacycle ring size: L5 > L6 > L7.

Treatment of the diphosphines ortho-B10H10C(PtBu2)C(PR2) (R = Et, Cy, Ph) with HCl gives the zwitterionic, nido-12-vertex species B10H10C(PHtBu2)C(PClR2); these reactions are reversed by the addition of NEt3.

The binuclear cyclometalates [Pt2Cl2{2-CMe2C6H4P(C6H4(2-iPr))2}2] (1a) and [Pt2Cl2{2-CMe2C6H3(4-OMe)P(C6H3(2-iPr)(4-OMe))2}2] (1b) react with CHCl2CHCl2 to give the corresponding mononuclear phosphine-alkene chelates [PtCl2{2-CH2═CMeC6H4P(C6H4(2-iPr))2}] (2a) and [PtCl2{2-CH2═CMeC6H3(4-OMe)P(C6H3(2-iPr)(4-OMe))2}] (2b). The product 2a can also be formed directly from [PtCl2(NCtBu)2] and La in CHCl2CHCl2 or by addition of SO2Cl2 to 1a. Addition of an excess of SO2Cl2 to 1b gave [PtCl2{2-CH2═CMeC6H3(4-OMe)P(C6H2(2-iPr)(4-OMe)(5-Cl))2}] (3b), a derivative of 2b featuring meta-chlorine substituents on the terminal P groups as a result of electrophilic aromatic substitution. A mechanism for the conversion of 1a,b to 2a,b is proposed involving an electrophilic alkyl C−H activation by a coordinatively unsaturated platinum(IV) species. The mechanism is supported by the isolation of the diplatinum(IV) cyclometalate [Pt2Cl2{2-CH2C6H3(4-OMe)P(C6H3(2-Me)(4-OMe))2}] as a mixture of syn and anti isomers 5b and 5b′. The crystal structures of 2a and 3b have been determined.

The secondary phosphine CgPH (CgP = 6-phospha-2,4,8-trioxa-1,3,5,7-tetramethyladamantyl group) is made in 50% yield by a modification of the literature method (avoiding high pressures of PH3) by bubbling PH3 through an acidified solution of 2,4-pentanedione at 0 °C. Under similar conditions the ethyl analogue EtCgPH is formed from 3,5-heptanedione in 75% yield. The halophosphines CgPCl and CgPBr are made by treatment of CgPH with N-halosuccinimide. CgPBr is also made by treatment of CgPH with Br2. Three methods are described for the synthesis of CgPR, where R = alkyl: (a) the previously reported acid-catalyzed condensation reaction of RPH2 with 2,4-pentanedione, which has been extended to R = iPr; (b) treatment of CgP(BH3)Li with RX followed by borane deprotection with Et2NH, which has been used for R = iPr, benzyl, n-C20H41; (c) treatment of CgPBr with RMgX, which has been used for R = iPr, Me. The complexes [PtCl2(CgPH)2] (1), [PdCl2(CgPH)2] (2), [PdCl2(CgPR)2] (where R = iPr (3a), Cy (3b)), and [PtCl2(CgPR)2] (where R = iPr (4a), Cy (4b), n-C20H41 (4c)) are described. The crystal structures of CgPH, CgPCl, [CgP(CH2Ph)2]Br, CgP(n-C20H41), and complexes 1, 3b, and 4c are reported. From the ν(CO) values for trans-[RhCl(CO)(CgPX)2], the σ-donor/π-acceptor properties of CgPX are in the order X = iPr > Me > Ph > H > Cl.

The 4-phosphacyclohexanones, 2,2,6,6-tetramethyl-1-phenyl-4-phosphorinanone (La), 1,2,6-triphenyl-4-phosphorinanone (PhLb), 1-cyclohexyl-2,6-diphenyl-4-phosphorinanone (CyLb) and 1-tert-butyl-2,6-diphenyl-4-phosphorinanone (BuLb) have been made by modifications of literature methods. Phosphines RLb are each formed as mixtures of meso- and rac-diastereoisomers. Isomerically pure rac-PhLb, rac-CyLb and meso-BuLb can be isolated by recrystallisation from MeCN. Heating mixtures of isomers of RLb with TsOH leads to isomerisations to give predominantly the meso-RLb. The complex trans-[PdCl2(La)2] (1) is readily made from [PdCl2(NCPh)2] but the analogous platinum complex 2 has not been detected and instead, cyclometallation at the 3-position (α to the ketone) in the phosphacycle occurs to give trans-[PtCl(La)(La–3H)] (3) (where La–3H = La deprotonated at the 3-position) featuring a [3.1.1]metallabicycle as confirmed by X-ray crystallography. The analogous palladabicycle 4 has been detected upon treatment of 1 with Et3N in refluxing toluene. The type of complex formed by RLb depends on which diastereoisomer (meso or rac) is involved. rac-PhLb (a mixture of R,R- and S,S-enantiomers, labelled α and β) forms trans-[MCl2(rac-PhLb)2], M = Pd (5) or Pt (6), as mixtures of diastereoisomers (αα/ββ and αβ forms). The structure of αα-6 has been determined by X-ray crystallography. Ligand competition experiments monitored by 31P NMR showed that Pd(II) and Pt(II) have a significant preference to bind rac-PhLb over meso-PhLb. meso-BuLb reacts with [PtCl2(NCBut)2] under ambient conditions to give the binuclear complex [Pt2Cl2(meso-BuLb-2′H)2] (7) where orthometallation has occurred on one of the exocyclic phenyl substituents as confirmed by X-ray crystallography. rac-BuLb reacts with [PtCl2(NCBut)2] to give a mononuclear cyclometallated species assigned the structure trans-[PtCl(rac-BuLb-2′H)(BuLb)] (8) on the basis of its 31P NMR spectrum. rac-CyLb reacts with [PtCl2(NCBut)2] in refluxing toluene to give trans-[PtCl2(rac-CyLb)2] (9) and the crystal structure of αβ-9 has been determined.

The cage phosphines 1,3,5,7-tetramethyl-6-phenyl-2,4,8-trioxa-6-phosphaadamantane (1a) and 1,3,5,7-tetraethyl-6-phenyl-2,4,8,trioxa-6-phosphaadamantane (1b) have been made by the acid catalysed addition of PhPH2 to the appropriate β-diketones; the acid used (HCl, H3PO4 or H2SO4) and its concentration affect the rate and selectivity of these condensation reactions. Phosphines 1a and 1b react with [PdCl2(NCPh)2] to form complexes trans-[PdCl2(1a)2] (2a) and trans-[PdCl2(1b)2] (2b) as mixtures of rac and meso diastereoisomers. The platinum(II) chemistry is more complicated and when 1a or 1b is added to [PtCl2(cod)], equilibrium mixtures of trans-[PtCl2L2] and [Pt2Cl4L2] (L = 1a or 1b) are formed in CH2Cl2 solution. Meso/rac mixtures of trans-[MCl(CO)(1a)2] M = Ir (6a) or Rh (7a) are formed upon treatment of MCl3·nH2O with an excess of 1a and the anionic cobalt complex [NHEt3][CoCl3(1a)] (9) was isolated from the product formed by CoCl2·6H2O and 1a. The νCO values from the IR spectra of 6a and 7a suggest that 1a resembles a phosphonite in its bonding to Rh and Ir. Crystal structures of meso-2a, meso-2b, rac-6a and 9 are reported and in each case a small intracage C–P–C angle of ca. 94° is observed and this may partly explain the bonding characteristics of ligands 1a and 1b. The cone angles for 1a and 1b are similar and large (ca. 200°). Rhodium complexes of ligands 1a and 1b are hydroformylation catalysts with similarly high activity to catalysts derived from phosphites. The catalysts derived from 1a and 1b gave unusually low linear selectivity in the hydroformylation of hexenes. This feature has been further exploited in quaternary-selective hydroformylations of unsaturated esters; catalysts derived from 1a give better yields and regioselectivities than any previously reported catalyst.

Palladium(II) complexes of ligands of the type Ar2PCH2- PAr2 and Ar2PN(Me)PAr2 (Ar = ortho-substituted phenyl group) are very efficient catalysts for copolymerisation of CO and C2H4.

Fast, selective conversion of internal olefins to linear esters is catalysed by Pd(II) complexes of chelating bis(phospha-adamantyl)diphosphines and the catalysis is acutely sensitive to the ligand backbone and even to the diastereomer used; the results are compared with those for the PBut2 analogue.

Rhodium(I) complexes of monodentate phosphonites derived from 2,2′-binaphthol and 9,9′-biphenanthrol are compared with diphosphonite chelate analogues as catalysts for asymmetric hydrogenation; the high ee’s (up to 92%) obtained with the monodentate systems and the observation that they are sometimes superior to the chelate analogues are discussed.

Rhodium complexes of unsymmetrical diphosphines of the type Ph2PCH2CH2PAr2 are catalysts for the carbonylation of methanol; several features of the catalysis are reminiscent of iridium carbonylation catalysts.

Enhancement of enantioselectivity in hydrogenations catalysed by δ vs. λ rhodium chelate complexes of trans-1,2-bis(phospholano)cyclopentanes cannot be rationalised using the current quadrant model for Duphos ligands and therefore a new consistent model is suggested.

Treatment of the diphosphines ortho-B10H10C(PtBu2)C(PR2) (R = Et, Cy, Ph) with HCl gives the zwitterionic, nido-12-vertex species B10H10C(PHtBu2)C(PClR2); these reactions are reversed by the addition of NEt3.

An efficient, classical resolution of the versatile P-ligand intermediate 6-phospha-2,4,8-trioxa-adamantane (CgPH) is described and the rhodium complex of the optically pure secondary phosphine β-CgPH is an active and moderately selective asymmetric hydrogenation catalyst.

The following unsymmetrical diphosphines have been prepared: o-C6H4(CH2PtBu2)(PR2) where R = PtBu2 (L3a3a3a); PCg (L3b3b); PPh2 (L3c3c3c); P(o-C6H4CH3)2 (L3d3d3d); P(o-C6H4OCH3)2 (L3e3e) and o-C6H4(CH2PCg)(PCg) (L3f3f) where PCg is 6-phospha-2,4,8-trioxa-1,3,5,7-tetramethyladamant-6-yl. Hydromethoxycarbonylation of ethene under commercially relevant conditions has been investigated in the presence of Pd complexes of each of the ligands L3a–f3a–f and the results compared with those obtained with the commercially used o-C6H4(CH2PtBu2)2 (L1a1a). The Pd complexes of the bulkiest ligands L3a3a3a, L3b3b and L3f3f are highly active catalysts but the Pd complexes of L3c3c3c, L3d3d3d and L3e3e are completely inactive. The crystal structures of the complexes [PtCl2(L1a1a)] (1a) and [PtCl2(L3a3a3a)] (2a) have been determined and show that the crystallographic bite angles and cone angles are greater for L1a1a than L3a3a3a. Solution NMR studies show that the seven-membered chelate in 1a is more rigid than the six-membered chelate in 2a. Treatment of [PtCl(CH3)(cod)] with L3a–f3a–f gave [PtCl(CH3)(L3a–f3a–f)] as mixtures of 2 isomers 3a–f and 4a–f. The ratio of the products 4:3 ranges from 100:1 to 1:20, the precise proportion is apparently governed by a balance of two competing factors, steric bulk and the antisymbiotic effect. The palladium complexes [PdCl(CH3)(L3b3b)] (5b/6b) and [PdCl(CH3)(L3c3c3c)] (5c/6c) react with labelled 13CO to give the corresponding acyl species [PdCl(13COCH3)(L3b3b)] (7b/8b) and [PdCl(13COCH3)(L3c3c3c)] (7c/8c). Treatment of [PdCl(13COCH3)(L)] with MeOH gave CH313COOMe rapidly when L = L3b3b but very slowly when L = L3c3c3c paralleling the contrasting catalytic activity of the Pd complexes of these two ligands.

The fluoroaryl phosphines P{C6H3(CF3)2-3,5}3 (Laa) and P(C6F5)3 (Lbb) form the complexes trans-[MCl2(Laa)2] and trans-[MCl2(Lbb)2] (M = Pd or Pt) which have been isolated and fully characterised. 31P NMR studies of competition experiments show that the stability of trans-[PdCl2L2] is in the order L = Lbb < Laa < PPh3. The crystal structure of trans-[PtCl2(Laa)2] is reported and reveals that the Pt–P bond lengths in trans-[PtCl2L2] are in the order L = Lbb < Laa < PPh3. The equilibria established when [Pt(norbornene)3] is treated with Laa or Lbb are investigated by 31P and 195Pt NMR spectroscopy and the species [PtLn(norbornene)3−n] (n = 1–3) identified. Ligands Laa and Lbb appear to have similar affinities for platinum(0). The complexes trans-[MCl(CO)(Laa)2] and trans-[MCl(CO)(Lbb)2] (M = Rh or Ir) have been synthesised and fully characterised; the values of νCO are comparable with those for analogous phosphite complexes. The ligands Laa, Lbb, P(C6H2F3-3,4,5)3 (Lccc), P{C6H4(CF3)-2}3 (Ldd), PPh3 and P(OPh)3 have been tested in rhodium-catalysed hydroformylation of 1-hexene and Laa, Lbb, and PPh3 have been tested in rhodium-catalysed hydroformylation of 4-methoxystyrene. Ligands Laa, and Lbb, have been shown to be stable under the hydroformylation catalysis conditions. For the 1-hexene reaction, the activity and selectivity for Laa and Lccc are very similar to the PPh3 catalyst (TOF ca. 400 h−1; n : iso 2.5–3.0) but for the sterically demanding Lbb and Ldd the activity and selectivity was much lower than with PPh3 (TOF ca. 15, n : iso ratio 0.6). Thus, the yield of heptanals obtained with the catalyst derived from Laa is 94% while under the same conditions with Lbb only 6%. The TOF for the Laa/Rh catalyst was 5 times lower than for the P(OPh)3/Rh catalyst despite the superficially similar ligand electronic characteristics for Laa and P(OPh)3.

The synthesis of a series of CgPAr ligands is reported, where CgP is the 6-phospha-2,4,8-trioxa-1,3,5,7-tetramethyladamant-6-yl moiety and Ar = 2-pyridyl (L2), 3-pyridyl (L3), 2-pyrimidyl (L4), 4-R-2-pyridyl [R = Me (L5a), CF3 (L6a), SiMe3 (L7a)] or 6-R-2-pyridyl [R = Me (L5b), CF3 (L6b), SiMe3 (L7b). Testing of these ligands in the Pd-catalysed methoxycarbonylation of phenylacetylene reveals that the activity and branched selectivity of the catalysts derived from these ligands varies as a function of the N-heterocycle, with the catalyst derived from L5b being the most active of those tested. This, together with the poor performance of catalysts derived from L3 supports the hypothesis that the catalysis proceeds by a “proton shuttling” mechanism, an idea that previously had only been applied to arylphosphines. Reaction of [PtCl2(cod)] with L where L = L2 or L4–7 yields a rac/meso mixture of the trans-[PtCl2(L)2] (1a–h) complexes, three of which are structurally characterised. 31P NMR spectroscopy shows that reaction of L3 with [PtCl2(cod)] gives a mixture of mononuclear and binuclear metal complexes in solution. The complex trans-[PdCl2(L2)2] (4) reacts with AgBF4 to give the [PdCl(κ1-L2)(κ2-L2)]BF4 (5) with spectroscopic and structural characterisation confirming the presence of a P,N-chelate. 1H and 31P NMR evidence supports the assignment of a pyridyl-protonated species being formed upon treatment of 4 with TsOH·H2O in CD2Cl2; both the protonated species and chelate 5 are observed when the reaction is carried out in MeOH.

Correction for ‘Reversible CO exchange at platinum(0). An example of similar complex properties produced by ligands with very different stereoelectronic characteristics’ by Sebastian J. K. Forrest et al., Dalton Trans., 2014, DOI: 10.1039/c4dt02303j.

The homologous series of diphosphines (CH2)n−1P(CH2)3P(CH2)n−1 where n = 5 (L5), 6 (L6), or 7 (L7) have been synthesized from the corresponding PhP(CH2)n−1. Treatment of [PtCl2(cod)] with L5–7 gave the 6-membered chelates cis-[PtCl2(L5–7)], the crystal structures for which reveal that L5–7 have very similar steric bulk and bite angles. Treatment of [Rh2Cl2(CO)4] with L5–7 gave the binuclear trans-[Rh2Cl2(CO)2(μ-L5–7)2] with syn and anti orientations of the CO and Cl ligands suggested by the 31P NMR spectra and the crystal structures of syn–trans-[Rh2Cl2(CO)2(μ-L5)2] and anti–trans-[Rh2Cl2(CO)2(μ-L7)2]. The ν(CO) values for trans-[Rh2Cl2(CO)2(μ-L5–7)2] indicate that the donor strength increases in the order L5 < L6 < L7. A study of rhodium-catalysed hydroformylation of 1-octene using diphosphines L5–7 is described. The catalyst activity decreases with increasing phosphacycle ring size: L5 > L6 > L7.

Substantially more active iron catalysts for a standard Negishi cross-coupling are obtained when bis(diarylphosphino)thiophenes are employed in place of the benchmark ligand bis(diphenylphosphino)benzene. The thiophene ligands have the advantages of ease of synthesis and ready modification.

The reaction of tetrasulfonated calix[4]arene (trioctylammonium salt) with P(NMe2)3 followed by treatment with gaseous NMe2H gave a zwitterionic six-coordinate phosphorus(V) species 1 containing a P(H)(NHMe2) group which can be stored for months without decomposition. In water, 1 loses NHMe2 and rearranges to form the water soluble phosphite Lcc. Phosphite Lcc has a half-life in water of ca. 5 h decomposing to H3PO3 and free tetrasulfonated calix[4]arene. Compound 1 serves as a convenient precursor to Lcc and complexes of Lcc are formed by dissolving 1 in water in the presence of labile metal complexes. The products have been identified by comparison of their 31P NMR data with well established analogues of calix[4]arene derived phosphites. In this way the water soluble complexes [Rh(acac)(CO)(Lcc)2] (2c) [Rh2Cl2(CO)2(Lcc)2] (3c), [Pt2Cl4(Lcc)2] (4c) and [PtCl2(Lcc)2] have been tentatively identified. The rhodium complex 3c has a half-life in water of 4 months. Two-phase (water/toluene) hydroformylation of 2-methylpentenoate with 2c as a catalyst has been investigated and the results compared with the same reaction in toluene with lipophilic analogues of 2c. Under mild conditions, with 2ccatalyst, branched aldehydes are the only products of hydroformylation and one of the branched aldehydes is selectively hydrogenated to give the lactone derivative.

A chlorosilane elimination reaction has been developed that allows the efficient synthesis of optically pure C1-symmetric, C1-backboned diphosphines with a wide variety of stereoelectronic characteristics.

9-Amino-9-phosphabicyclo[3.3.1]nonanes, (PhobPNHR′; R = Me or iPr) are readily prepared by aminolysis of PhobPCl and are significantly less susceptible to hydrolysis than the acyclic analogues Cy2PNHR′. Treatment of Cy2PNHMe with Cy2PCl readily gave Cy2PNMePCy2. By contrast, treatment of PhobPCl with PhobPNHMe in the presence of Et3N does not afford PhobPNMePPhob but instead the salt [PhobP(NMeH)PPhob]Cl is formed which, upon addition of [PtCl2(NCtBu)2] gives the zwitterionic complex [PtCl3(PhobP(NMeH)PPhob)]. The neutral PhobP(NMe)PPhob is accessible from PhobNMeLi and is converted to the chelate [PdCl2(PhobPNMePPhob)] by addition of [PdCl2(cod)]. The anomalous preference of the PhobP group for the formation of PPN products is discussed. The unsymmetrical diphos ligands PhobPNMePAr2 (Ar = Ph, o-Tol) are prepared, converted to [Cr(CO)4(PhobPNMePAr2)] and shown to form Cr-catalysts for ethene oligomerisation, producing a pattern of higher alkenes that corresponds to a Schulz-Flory distribution overlaid on selective tri/tetramerisation.

Azaborinylphosphines are readily prepared by the reaction of silylphosphines with a chloroborane under mild conditions; they are shown to contain P–B bonds that are sufficiently robust to allow these ligands to be used in homogeneous catalysis.

The homodiphosphanes CgP–PCg (1) and PhobP–PPhob (2) and the heterodiphosphanes CgP–PPhob (3), CgP–PPh2 (4a), CgP–P(o-Tol)2 (4b), CgP–PCy2 (4c), CgP–PtBu2 (4d), PhobP–PPh2 (5a), PhobP–P(o-Tol)2 (5b), PhobP–PCy2 (5c), PhobP–PtBu2 (5d) where CgP = 6-phospha-2,4,8-trioxa-1,3,5,7-tetramethyladamant-9-yl and PhobP = 9-phosphabicyclo[3.3.1]nonan-9-yl have been prepared from CgP(BH3)Li or PhobP(BH3)Li and the appropriate halophosphine. The formation of 1 is remarkably diastereoselective, with the major isomer (97% of the product) assigned to rac-1. Restricted rotation about the P–P bond of the bulky meso-1 is detected by variable temperature 31P NMR spectroscopy. Diphosphane 3 reacts with BH3 to give a mixture of CgP(BH3)–PPhob and CgP–PPhob(BH3) which was unexpected in view of the predicted much greater electron-richness of the PhobP site. Each of the diphosphanes was treated with dimethylacetylene dicarboxylate (DMAD) in order to determine their propensity for diphosphination. The homodiphosphanes 1 and 2 did not react with DMAD. The CgP-containing heterodiphosphanes 4a–d all added to DMAD to generate the corresponding cisalkenes CgPCH(CO2Me)CH(CO2Me)PR2 (6a–d) which have been used in situ to form chelate complexes of the type [MCl2(diphos)] (7a–d) where M = Pd or Pt. The PhobP-containing heterodiphosphanes 3 and 5a–d react anomalously with DMAD and do not give the products of diphosphination. The X-ray crystal structures of the diphosphanes 2, 3, 4a, and 5a, the monoxide and dioxide of diphosphane 1, and the platinum chelate complex 7c have been determined and their structures are discussed.