Phosphido bridged metal complexes

Even chlorine which is bound to phosphorus coordinated to a metal atom can be exchanged for fluorine, but higher temperatures are required. So the four-membered phosphido-bridged metal complex 16 is fluorinated at temperatures over 100C, whereas the exchange reaction in the case of the corresponding iodide proceeds at room temperature and for the bromide at over 60CC in 80% yield each.77... 

In bridged metal-metal bonded dimeric complexes, the relative importance of metal-metal and bridging ligand effects are more difficult to unravel. Dahl and his co-workers have elegantly exploited systematic crystallographic analyses to detail the stereochemical consequences of valence-electron addition or removal in dimeric metal complexes (46, 47, 65, 230) and clusters (66, 88, 204, 205, 213, 216, 222). Their experimental work has been neatly underpinned by nonparameterized approximate Hartree-Fock molecular orbital calculations (217) on the phosphido-bridged dimers [Cr2(CO)80ti-PR2)2]n"2 and [Mn2(CO)g(/i.-PR2)2]n (rt = 0, + 1, or +2) ... 

Metal-chromium phosphido-bridged complexes, with carbonyls, 5, 217... 

Varieties of dinuclear cobalt complexes are known with two phosphido bridges. Those so far reported with the di-terf-butylphosphido ligand have two pseudotetrahedral 18-electron Co atoms linked by a metal-metal bond formally of order 2. Tetracarbonylbis(ii-di-terf-butylphosphido)-dicobalt( -t-1) can be prepared from the reaction of Co(CO)4l (generated in situ) with Li(r-Bu2P) in THE We describe here a simplified, high yield synthesis of this dimer via the interaction of Co2(CO)g with r-Bu2PH in toluene. The complex should prove to be a useful starting material for further reactivity studies. 

It is against this background that we have developed in our laboratories a very simple one-step procedure which allows the synthesis, usually in acceptable yields, of a wide variety of and M -dppm-CO mono- and (more usually) binuclear complexes directly from metal salts. The procedure has been extendi with considerable success to the one-step synthesis of certain heterobinuclear systems and also some phosphido-bridged complexes of Co and Np. While this study has so far been largely concerned with Co and systems, preliminary work has been carried out with Rh , Pd and Fe . Some of the work described herein has been reported in preliminary communications but a complete overview of all aspects of the investigations carried out so far is given here in order that the very broad applicability of the procedure can be fully appreciated. 

While, because of our interest in bimetallic species, most of the work discussed in this account has concentrated upon reactions which involve dppm, the synthetic procedure outlined clearly represents a novel and extremely simple approach to metal carbonyl phosphine complexes in general. Of particular significance, however, are the one-step reactions which lead to heterobimetallic or phosphido-bridged complexes and the ready access to palladium carbonyl complexes. Further research in this area is likely to be extremely productive. 

A study of nucleophilic addition by PhLi to the bimetallic complexes [(CO)4M(/A-PPh2)2Pt(PCy3)] (54), M = Mo or W, reveals differences in regio-specificity compared to mononuclear octahedral metal carbonyl substrates. Addition of PhLi occurs on an equatorial CO of (54) (trans to the phosphido bridge). 

---