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

Addition of the silane (HSiMe 2 )C 2 B 10 H 10 (PR 2 ) (R = Me ( 2a ), OEt ( 2b )) to (PPh 3 ) 2 Pt(CH 2 CH 2 ) ( 3 ) affords the trans -bis(chelates) Pt(Cab P,Si ) 2 ( 4a, b; Cab P,Si = η 2 -[(SiMe 2 )(PR 2 )C 2 B 10 H 10 - P,Si ]) in high yield; the same product was also formed from Pt(cod) 2 ( 9 ), as confirmed by NMR spectroscopy ( 1 H, 31 P). Using Pd 2 (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 ( 1 H, 31 P). Thus, a series of kinetically stabilized trans -bis(chelate) metal complexes, trans -(Cab P,Si ) 2 M (M = Pt ( 4a, b ), Pd ( 7a )), bearing bulky o -carboranylphosphine tethers, were synthesized from the reaction of phosphinosilanes ( 2 ) with d 10 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 ) 2 Pt ( 5a, b ). In addition, the oxidative addition of the Si−H bond to the sterically bulky diphenylphosphino silane (HSiMe 2 )C 2 B 10 H 10 (PPh 2 ) ( 2c ) by 3 can be controlled to produce the mono(chelate) species (Cab P,Si )Pt(H)(PPh 3 ) ( 10a ). The related mono(chelate) product (Cab P,Si )Pt(H)(Cab P ) ( 10b; Cab P = (PPh 2 )C 2 B 10 H 11 ) results from the oxidative addition of 2c by 3, in which one PPh 3 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.