Agostic Interactions in Phosphine Complexes

C-H agostic interaction from a pendant alkyl (dRuC = 2.588 A) and a weaker interaction from a phosphine methyl group (dRuC = 3.049 A).57 

Mn systems contrast with the neutral Mo(CO)(PP)2 analogues, which contain only one interaction from either a phenyl C-H (12) or an isobutyl y-C-H (13). 

Steric factors are critical (see below) and are no doubt responsible for the long M H-C distances in the rigid chelate systems, which do not allow easy approach 

The agostic bonding in [RuH(dppp)2]+ is noteworthy in that the overall geometry (14) differs from that of the corresponding H2 complex, which has the usual trans geometry (15).56 The octahedral geometry in 14 also contrasts to that in 

Formally 14e complexes with two open sites possess polyagostic interactions that are stronger than those in less unsaturated 16e systems., 60,61 A fourfold interaction (two - - -phenyl-H and two M-f-butyl-H) exists in M(PPh Bu2)2 (M = Pt, Pd estimated M H = 2.5-2.6 A), and [Ru(Ph)(CO)(P Bu2Me)2] +has two Ru H C interactions originating from one Bu on each phosphine.61 The preference for donation from Bu over Me substituents is attributed to better steric approach of the former (giving a five-membered ring) than the latter (four-mem- 

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