Bridged phosphine complexes

Figure 3.38 Synthesis of the halogen-bridged 1 1 phosphine complexes.

Zhang, H.-X. and Che, C.-M. (2001) Aurophilic Attraction and Luminescence of Binuclear Gold(I) Complexes with Bridging Phosphine Ligands ah initio Study. Chemistry - A European Journal, 7, 4887-4893. 

Pan, Q.-J. and Zhang, H.-X. (2003) Aurophilic attraction and excited-state properties of binuclear Au(I) complexes with bridging phosphine and/or thiolate ligands An ah initio study. Journal of Chemical Physics, 119, 4346-4352. 

Examples are tending to be more sophisticated and complex in form. For example, a dinuclear complex featuring a bridging phosphinate and phenolate in addition to peroxide (221) has been reported,966 as a model for phosphodiester systems. Apart from dicobalt(III) systems, a mixed-valence CoII,ni di-/i-superoxo complex (222) has been prepared.967 Transition between the three redox states CoII,n, Co11,111, and Co111111 is electrochemically reversible. 

Balch, A. L. Binuclear, phosphine-bridged complexes progress and prospects. Pignoler, L. H. Ed. Homogenous Catal. Met. Phosphine Complex. 1983, 167, Plenum New York, 1983. 

It was recognized during the development of propene hydroformylation that propene provided some stabilization for the catalyst. In the absence of the alkene, but in the presence of carbon monoxide and hydrogen, the catalyst can undergo what has been termed intrinsic deactivation. [3 3] Apparently after oxidative addition of triphenyl-phosphine to rhodium, diphenylphosphido bridged rhodium complexes are formed. 

Phosphorus ligands are shown from NMR studies to take up equatorial positions, while pyridine and isonitrile bond to axial sites. For axial substitution, two isomers occur, depending on the orientation relative to the bridging hydrogen atom. The phosphine complexes lose CO on heating to yield the "unsaturated complexes H2Os3(CO)9L... 

The observed first-order rate constants, Kobs (s ) for the reaction of the rhodium] 11) complexes with diazo ester 34 varied over a range of > 10, in which the pivalate catalyst (entry 3) was almost two orders of magnitude faster than any of the other catalysts studied. The carboxamidate catalysts (entries 8-10) were slower than all the carboxy-lates, while the bridged phosphine catalyst (entry 7) behaved like most of the other car-boxy late s. 

---