Synthesis, Structure, and DFT Calculation of (Phosphino-o-carboranyl)silyl Group 10 Metal Complexes:  Formation of Stable trans-Bis(P,Si-chelate)metal Complexes

Addition of the silane (HSiMe2)C2B10H10(PR2) (R = Me (2a), OEt (2b)) to (PPh3)2Pt(CH2CH2) (3) affords the trans-bis(chelates) Pt(Cab P,Si )2 (4a,b; Cab P,Si = η2-[(SiMe2)(PR2)C2B10H10-P,Si]) in high yield; the same product was also formed from Pt(cod)2 (9), as confirmed by NMR spectroscopy (1H, 31P). Using Pd2(dba)3 (6), the analogue trans-bis(chelate) Pd(Cab P,Si )2 (7a) was obtained as a mixture of trans and cis isomers in which the former predominates, as established by NMR spectroscopy (1H, 31P). Thus, a series of kinetically stabilized trans-bis(chelate) metal complexes, trans-(Cab P,Si )2M (M = Pt (4a,b), Pd (7a)), bearing bulky o-carboranylphosphine tethers, were synthesized from the reaction of phosphinosilanes (2) with d10 metal complexes. In the presence of dimethyl acetylenedicarboxylate (DMAD), the trans isomer 4a,b thermally rearranges to the thermodynamically favored cis isomer cis-(Cab P,Si )2Pt (5a,b). In addition, the oxidative addition of the Si−H bond to the sterically bulky diphenylphosphino silane (HSiMe2)C2B10H10(PPh2) (2c) by 3 can be controlled to produce the mono(chelate) species (Cab P,Si )Pt(H)(PPh3) (10a). The related mono(chelate) product (Cab P,Si )Pt(H)(Cab P ) (10b; Cab P = (PPh2)C2B10H11) results from the oxidative addition of 2c by 3, in which one PPh3 ligand is displaced by Cab P . The structures of compounds 4a, 5a,c, 8c, and 10a,b were determined using single-crystal X-ray crystallography.