The reaction of Sm{N(SiMe3)2}3 with the bis(phenol)amines H2O2NR (H2O2NR = RCH2CH2N(2-HO-3,5-C6H2tBu2)2; R = OMe, NMe2 or Me) gave exclusively zwitterions Sm(O2NR)(HO2NR). For R = OMe or NMe2 these were efficient catalysts for the ring-opening polymerisation of ε-caprolactone and D,L-lactide with a tendency to form cyclic esters; in contrast, no polymerisation was observed for R = Me.

Reactions of the imido complex Cp(ArN)Ta(PMe3)2 (1, Ar = 2,6-diisopropylphenyl) with silanes afford the silyl hydrides Cp(ArN)Ta(PMe3)(H)(SiRnCl3−n) (2b−e) and Cp(ArN)Ta(PMe3)(H)(SiPhMeH) (2a) as the first kinetic products. However, the hydride compounds Cp(ArN)Ta(PMe3)(H)(SiRnCl3−n) are metastable and, first, rearrange in the presence of phosphine to the chlorides Cp(ArN)Ta(PMe3)(Cl)(SiHRnCl2−n) (5) and then decompose to Cp(ArN)Ta(PMe3)(Cl)(H) (4) and eventually to Cp(ArN)Ta(PMe3)Cl2 (3). Complexes with a smaller Ar′ substituent at nitrogen (Ar′ = 2,6-dimethylphenyl) react faster, as do more Lewis acidic silanes. The occurrence of interligand hypervalent interactions in the tantalum complexes Cp(ArN)Ta(PMe3)(H)(SiRnCl3−n) has been revealed by X-ray structure analysis, DFT calculations, and the experimental determination of the sign of the coupling constant J(Si−H). The J(Si−H) was found to be negative for Cp(ArN)Ta(PMe3)(H)(SiMenCl3−n) (J(Si−H) = −40 Hz for n = 1; J(Si−H) = −50 Hz for n = 0), indicative of the presence of Si−H bonding, but positive for Cp(ArN)Ta(PMe3)(H)(SiMeHPh) (J(Si−H) = +14 Hz), suggesting the absence of direct Si−H interactions. A DFT study of the mechanism of silane coupling with the model imido complex Cp(MeN)Ta(PMe3)2 established the feasibility of the direct addition of silanes HSiMenCl3−n (n = 1−3) to the imido group to give the adduct Cp(MeN{→SiR3-H})Ta(PMe3)2, as previously found in the related niobium chemistry.

The imidotungsten dimethyl compound [W(N2Npy)(NPh)Me2] 2 reacts with BArF3 to form the cationic complex [W(N2Npy)(NPh)Me]+ 3+ [anion = [MeBArF3]−; ArF = C6F5; N2Npy = MeC(2-C5H4N)(CH2NSiMe3)2] which undergoes methyl group exchange with added 2, [Cp2ZrMe2] or ZnMe2; treatment of cation 3+ with CO2 or isocyanates leads to cycloaddition reactions at the WNPh bond and not insertion into the W–Me bond, despite the latter product being the most thermodynamically favourable according to DFT calculations.

Reaction of the cyclopentadienyl–amidinate supported imidotitanium complexes [Ti(η-C5Me5){MeC(NiPr)2}(NR)] (R = tBu 1a or Ar 1b where Ar = 2,6-C6H3Me2) with CO2 proceed via initial cycloaddition reactions, but depending on the imido N-substituent go on to yield products of either isocyanate extrusion or double CO2 insertion, the latter forming [Ti(η-C5Me5){MeC(NiPr)2}{O(CO)N(Ar)(CO)O}] 4; the double CO2 insertion reaction leading to 4 is the first example for any transition metal imide.

Straightforward, multigram synthesis of the new diamide–diamine proligand H2N2NN′ [N2NN′ = (2-NC5H4)CH2N(CH2CH2 NSiMe3)2] is described along with a preliminary survey of the five- and six-coordinate, neutral and cationic, single- and multiply-bonded complexes of groups 3, 4 and 5 that it can support; the related bis(alkoxide)–diamine proligand H2O2NN′ is also described where H2O2NN′ = (2-NC5H4)CH2N(CH2CMe2 OH)2.

The reaction of Sm{N(SiMe3)2}3 with the bis(phenol)amines H2O2NR (H2O2NR = RCH2CH2N(2-HO-3,5-C6H2tBu2)2; R = OMe, NMe2 or Me) gave exclusively zwitterions Sm(O2NR)(HO2NR). For R = OMe or NMe2 these were efficient catalysts for the ring-opening polymerisation of ε-caprolactone and D,L-lactide with a tendency to form cyclic esters; in contrast, no polymerisation was observed for R = Me.