Mechanisms of C−C and C−H Alkane Reductive Eliminations from Octahedral Pt(IV): Reaction via Five-Coordinate Intermediates or Direct Elimination?

The Pt(IV) complexes P2PtMe3R [P2 = dppe (PPh2(CH2)2PPh2), dppbz (o-PPh2(C6H4)PPh2); R
= Me, H] undergo reductive elimination reactions to form carbon−carbon or carbon−hydrogen bonds.
Mechanistic studies have been carried out for both C−C and C−H coupling reactions and the reductive
elimination reactions to form ethane and methane are directly compared. For C−C reductive elimination,
the evidence supports a mechanism of initial phosphine chelate opening followed by C−C coupling from
the resulting five-coordinate intermediate. In contrast, mechanistic studies on C−H reductive elimination
support an unusual pathway at Pt(IV) of direct coupling without preliminary ligand loss. The complexes
fac- P2PtMe3R (P2 = dppe, R = Me, H; P2 = dppbz, R = Me) have been characterized crystallographically.
The Pt(IV) hydrides, fac-P2PtMe3H (P2 = dppe, dppbz), are rare examples of stable phosphine ligated
Pt(IV) alkyl hydride complexes.