A carbon(0)-bridged Pt2Ag2 cluster was synthesized from the reaction of a cyclometalated pincer carbodiphosphorane platinum complex with AgOTf, by forming Pt(II)←C(0)→Ag(I) dative bonds along with Pt(II)–Ag(I) and Ag(I)–Ag(I) metal–metal interactions. X-ray diffraction analysis reveals that the cluster adopts an antiparallel sandwich structure with a ladder-shaped PtC/AgAg/CPt core. The coordination plane of the platinum unit is highly distorted due to the in-plane steric repulsion between the PEt3 ligand on the platinum and the nearest proton on each of the two cyclometalated phenyl rings in the pincer carbodiphosphorane framework. The cluster is very labile and displays different reactivity patterns toward trivalent phosphorus ligands. In the reaction with bulky PPh3, a dinuclear complex was formed because of coordination of PPh3 to the silver atom upon cleavage of the tetranuclear core. In contrast, replacement of the PEt3 on the platinum center by P(OPh)3, which is sterically less demanding, led to a dinuclear complex where the eliminated PEt3 ligand recoordinated to the silver atom.

Two novel chloride-centered Ag18 clusters with the same framework but different supporting phosphines are synthesized by the reaction of PhCCAg, AgSbF6, PPh3 (or P(p-Tol)3), and NaBH4 in CH2Cl2, followed by the addition of PhCCH and NEt3. The inner twelve Ag atoms of these two clusters are arranged in a rare cuboctahedral structure, which can be rationalized by considering a ligand effect. Through careful analysis, we find that the central chloride arises from a generally ignored but nonetheless existing reaction between CH2Cl2 and NEt3, which is well recognized as the Menshutkin reaction. This research provides insights into the dependence of the cluster structure on the nature of the ligand and into the cluster formation mechanism of the Menshutkin reaction.

A synthetic route was developed for a novel bicyclic diphosphine 5 in which two structurally robust 1,8-naphthalenediyl groups clamp the P–P bond of the diphosphine to form a butterfly structure. The bicyclic framework was synthesized by a ring-opening dimerization of a strained four-membered phosphacycle of iPr2NP-peri-bridged naphthalene 8. A toluene solution of 8 was heated for 2 days in the presence of O2 and one equivalent of H2O to give a mixture of oxides of the target diphosphine 5, then the mixture of oxides was reduced with HSiCl3 to afford 5 in a moderate yield. The crystal structure of 5 confirmed that the P–P bond and the two naphthalene groups form a butterfly molecular structure, and the two lone pairs on the respective phosphorus centers are disposed in a synperiplanar configuration. These two phosphorus donor atoms bind two AuCl fragments to form a unique “U-shape” binuclear complex (μ-5)-[AuCl]2 in which the two Au(I) centers are separated by ca. 4.4 Å that indicates the negligible intramolecular Au–Au interaction. In the crystal, the two binuclear complexes interlocked with each other through multiple intermolecular Au–Au interactions between the two U-shape units.Dimerization reaction of phosphorus-atom peri-bridged naphthalene having a strained four-membered heterocycle gave bis(1,8-naphthalenediyl)diphosphine, in which the two lone pairs on the respective phosphorus centers are disposed in a synperiplanar configuration.

Commercially available THF solutions of BH3·THF, which contain 0.5 mol % of NaBH4 as a stabilizing reagent for BH3·THF, react with 1 atm of CO2 at room temperature to form trimethoxyboroxine, (MeOBO)3, in 87% yield after 12 h. Since no reaction took place in the absence of NaBH4, NaBH4 was found to work as a promoter or catalyst for the reduction of CO2 with BH3 to the methoxy compound. A similar reaction using HCOONa in place of NaBH4 also gave (MeOBO)3 in comparable yield.

A family of P-iron-substituted phosphinoboranes, Cp(CO)2Fe{P(Ar)BMes2} (Ar = Ph, Mes, Tipp, Mes*), have been prepared from the reaction of Cp(CO)2FeCl and (Li)(Ar)PBMes2. All the complexes have been characterized successfully by 1H, 11B, and 31P NMR; IR spectroscopy; and X-ray crystallography. In the IR spectra, all the complexes display similar carbonyl stretching frequencies that are remarkably higher than those of closely related phosphide complexes. These observations indicate that a repulsive interaction between the filled d orbital on the iron and the lone pair on the phosphorus is less severe in the studied iron-phosphinoboranes, which is most likely because of the P→B π interaction that occurs in them. The 31P{1H} NMR chemical shifts of the phosphinoborane phosphorus move upfield with the increasing steric bulk of the Ar groups in the order Ph (−51.4 ppm) < Mes (−68.8 ppm) < Tipp (−84.9 ppm). However, the phosphorus bearing the most sterically demanding Mes* group appears at an unexpectedly downfield value of −44.9 ppm, which is probably reflective of its structural peculiarities. The 1H NMR spectrum of each complex displays two sets of signals, assignable to inequivalent Mes groups on the boron atom, as a consequence of a hindered rotation around the P–B bond. This high rotational barrier most likely results from the significant double-bond character in the P–B bond. The X-ray diffraction studies have confirmed the iron-phosphinoboranes considered herein to be monomeric species. Each molecule consists of a nearly planar phosphinoborane fragment with a short P–B bond. The Fe–P bond is notably elongated as the Ar group becomes larger, demonstrating its somewhat vulnerable nature with respect to steric congestion. In contrast, the variation in the P–B bond distance is relatively small throughout the series of iron-phosphinoboranes, suggesting that the P═B double-bond character is balanced by steric and electronic effects of the substituents around the phosphorus.

A large-hole tetraphosphamacrocycle 2, with four phosphorus centers separated at the corners of a 3.7 Å wide and 9.7 Å long rectangle, was synthesized by a stepwise cyclization reaction between PCl-bridged [1.1]ferrocenophane and bisphenol A in a 2:2 ratio. The macrocycle 2 could incorporate two Ag+ or Pt0 fragments in the hole to provide binuclear complexes, which were identified as μ-2-[Ag(NCMe)2]2(BF4)2 (3) and μ-2-[Pt(PhCCPh)]2 (5), respectively, using X-ray and spectroscopic analysis. The X-ray structure of 3 demonstrates that the macrocycle 2 serves as a framework in which two diphosphine silver units are aligned in a front-to-front style, while that of 5 indicates that 2 can also bind two bulky Pt(PhCCPh) fragments by the flexible change of its conformation.

The early−late heterobinuclear complexes Cp2M(μ-OPPh2)2PdMe2 (M = Ti (1), Zr (2), and Hf (3)) were synthesized by the reaction of PdMe2(tmeda) (tmeda = Me2NCH2CH2NMe2) with respective metallocene diphosphinite ligands Cp2M(OPPh2)2 prepared from Cp2MCl2 (M = Ti, Zr, and Hf) and LiOPPh2. The complexes 1−3 catalyzed the addition (hydrophosphinylation) of HP(O)Ph2 to 1-octyne to give mainly not the single-addition product n-Hex-CH═CHP(O)Ph2 (4a) or n-Hex-C{P(O)Ph2}═CH2 (4b) but the double-addition product n-Hex-CH{P(O)Ph2}CH2P(O)Ph2 (5) at 40 °C in low yields. The yield of 5 was, however, substantially improved to >95% for 2 and 3 when tertiary phosphine PR3 such as PMePh2 was added to the catalytic system. The stoichiometric reaction of the complexes 1−3 with the phosphorus substrate HP(O)Ph2 and PMePh2 afforded in situ the trinuclear complexes H(PMePh2)Pd(μ-OPPh2)3M(μ-OPPh2)3PdH(PMePh2), which were found to exhibit the high catalytic activities similar to those of their parent complexes 1−3 in the presence of PR3 and were thus proposed to be a practical catalyst. On the basis of the above findings, simple mixtures of mononuclear Cp2MCl2 and PdMe2(tmeda) complexes together with PMePh2 could be used successfully as precatalysts for the double hydrophosphinylation of 1-octyne with HP(O)Ph2 to give satisfactory results comparable to those attained with the preorganized binuclear complexes 2 and 3 with PMePh2 added.

Reactions of Pd(PPh3)4 with P(═E)(NiPr2)(naph) (6, E = S; 7, E = O) (naph = 1,8-naphthylene) having a strained four-membered P(V)-phosphacycle gave dimeric complexes [Pd{κ2P,C-μ2-PE- P(═E)(NiPr2)(naph)}(PPh3)]2 (9, E = S; 10, E = O), in which a Pd metal has been inserted into a P−C bond of the phosphacycle to form a phosphapalladacycle having a P(V) donor, and the two phosphapalladacycle units have been mutually bridged with E═P groups, as confirmed by X-ray structure analysis for thermodynamically more stable racemic isomers 9a and 10a. The meso-to-racemic isomerization observed for the simultaneously formed meso isomer 9b, and probably also for the corresponding meso isomer 10b, indicated partial dissociation of 9 and 10 taking place to their monomer units in solution, which were actually trapped as [Pd{κ2P,C-P(═E)(NiPr2)(naph)}(dppe)] by treatment with bidentate dppe (dppe = 1,2-bis(diphenylphosphino)ethane). On the other hand, a similar treatment of 9a with monodentate PMe3 and PEt2Ph resulted in a trivial substitution of both PPh3 ligands to give dimeric PMe3 and PEt2Ph analogues of 9a, respectively. 10a was found to react with O2 to form an unprecedented oxidation product, [Pd{κ2P,O-μ2-PO-PO(═O)(NiPr2)(naph)}(PPh3)]2, 17, in which an oxygen atom has been inserted into each P(V)−Pd bond. 9a and 10a exhibited moderate catalytic activities for a Heck reaction between PhI and styrene. The mercury test indicated that metallic Pd nanoparticles released from 9a and 10a would be practical catalysts.

Isolation and characterization were carried out for a novel tridentate ferrocenylphosphine macrocycle, (−PhPC5H4FeC5H4−)3, as follows. A photolytic ring-opening reaction of PPh-bridged [1]ferrocenophane in ether gave a mixture of its oligomers. After their sulfurization, GPC separation of low-molecular-weight species afforded two isomers of a macrocyclic trimer, 1,1′′:1′,1′′′′:1′′′,1′′′′′-tris(phenylthiophosphinidene)tris(ferrocene), in which three 1,1′-ferrocenediyl units and three P(S)Ph groups were alternately linked to form a macrocyclic ring. Although yields of both isomers were low (17% in total), they were successfully desulfurized in good yields without configurational inversion at their phosphorus centers by treatment with MeOTf/P(NMe2)3 (OTf = CF3SO3), to give the respective tridentate macrocyclic phosphine ligands. The molecular structure of one isomer (C3 isomer) with C3 symmetry was determined by X-ray analysis, while the other was identified as the Cs isomer on the basis of 1H, 13C, and 31P NMR data. When the C3 isomer was heated in toluene at around 80 °C, it isomerized gradually but almost completely to the Cs isomer with the activation energy ΔG350⧧ = 26.2 ± 0.6 kcal mol−1. The reaction of AgOTf with the C3 isomer in CH2Cl2 gave a mononuclear silver complex in which the C3 isomer encircled the Ag+ ion as a tridentate ligand. To our surprise, a similar reaction using the Cs isomer gave the same silver complex as above, indicating that a facile conversion of the Cs isomer to the C3 isomer took place upon coordination to the Ag+ ion at room temperature.

A bisphosphine in which a PhP–PPh bond bridges 1,8-positions of naphthalene, 1,2-dihydro-1,2-diphenyl-naphtho[1,8-cd]-1,2-diphosphole (1), was used as a bridging ligand for the preparation of dinuclear group 6 metal complexes. Free trans-1, a more stable isomer having two phenyl groups on phosphorus centers mutually trans with respect to a naphthalene plane, was allowed to react with two equivalents of M(CO)5(thf) (M = W, Mo, Cr) at room temperature to give dinuclear complexes (OC)5M(μ-trans-1)M(CO)5 (M = W (2a), Mo (2b), Cr (2c)). The preparation of the corresponding dinuclear complexes bridged by the cis isomer of 1 was also carried out starting from the free trans-1 in the following way. Mono-nuclear complexes M(trans-1)(CO)5 (M = W (3a), Mo (3b), Cr (3c)) which had been prepared by a reaction of trans-1 with one equivalent of the corresponding M(CO)5(thf) (M = W, Mo, Cr) complex, were heated in toluene, wherein a part of the trans-3a–c was converted to their respective cis isomer M(cis-1)(CO)5. Each cis trans mixture of the mono-nuclear complexes 3a–c was treated with the corresponding M(CO)5(thf) to give a cis trans mixture of the respective dinuclear complexes 2a–c. The cis isomer of the ditungsten complex 2a was isolated, and its molecular structure was confirmed by X-ray analysis, showing a shorter W⋯W distance of 5.1661(3) Å than that of 5.8317(2) Å in trans-2a.A bisphosphine in which a PhP–PPh bond bridges 1,8-positions of naphthalene, 1,2-dihydro-1,2-diphenyl-naphtho[1,8-cd]-1,2-diphosphole (1), was used as a bridging ligand for the preparation of dinuclear group 6 metal complexes (OC)5M(μ-1)M(CO)5 (M = W, Mo, Cr).

The trivalent phosphorus-bridged [2]ferrocenophane complex 2 having NEt2 groups on the respective phosphorus centers was prepared, and its reactions as a diphosphine ligand were examined for iron and chromium carbonyl complexes. Both the phosphorus centers of 2 coordinated to Fe(CO)4 fragments to form (μ-2)-[Fe(CO)4]2, while the bulkier Cr(CO)5 fragment formed only a monochromium complex [Cr(κ1-2)(CO)5]. Dissociation of CO from [Cr(κ1-2)(CO)5] changed the coordination mode of 2 from κ1 to κ2 to form [Cr(κ2-2)(CO)4] having a three-membered ring. A similar approach for the monoiron complex [Fe(κ1-2)(CO)4] did not afford a κ2 complex but instead an Et2NPC(O)PNEt2-bridged [3]ferrocenophane complex in which a CO fragment was inserted into the P–P bond of 2 and both the phosphorus centers coordinated to Fe(CO)3 as a chelate diphosphine. The reaction of this product with an Fe(CO)4 fragment gave μ-{Fe(C5H4PNEt2)2-κP:κP}-[Fe(CO)3]2 (8), in which one terminal CO and the CO group between the two phosphorus atoms were lost to give an [FeFe]hydrogenase mimic having a bis(phosphido)ferrocene chelate as a bridging unit. The two NEt2 groups of the bridging unit were expected to work as protonation sites. The protonated NEt2 groups contributed to an improvement in the reduction potential of the complex to a less negative area, i.e., −2.3 V for the free 8 to −1.0 V for the diprotonated 8. The catalytic reduction of the proton, however, required a more negative potential of −2.0 V, which is almost comparable to that of the phosphido-bridged [FeFe]hydrogenase model complex having no protonation site.