Complexes of Co and Rh

The title complexes, CpM(PMe3)2 and CpM[P(OMe)3]2, are electron-rich half-sandwich complexes that have been demonstrated to be valuable pre- 

Note In the original procedure, the cycloocta-1.5-diene complex [CgHi2RhCl]2 was used as starting material. The present method avoids the isolation of the intermediate [Rh(PMe3)4]Cl. 

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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. 

Due to the stability of Ir complexes, catalytic activity of Ir complexes are usually lower than the corresponding Rh ones. Thus, the reported examples of catalytic reactions by Ir complexes are fewer than those of Co and Rh. 

Distributions of this type are traditionally interpreted as the result of particulate scavenging in surface waters followed by remineralization at depth. Type of distribution contrasts strongly with that of Co, the first series transition metal which is located directly above Rh in the periodic table, illustrates that elements from the same group in the periodic table can exhibit very different chemical behavior. The contrasting behavior of Co and Rh is potentially related to the fact the Co has an active redox chemistry in the marine environment whereas Rh is believed to be stable only as Rh(III) complexes. It is unclear why the upper crustal partition coefficient calculated for Rh is so large (Figure 1) by analogy to other trivalent metals a much lower value would be expected. 

The ligand field treatment has been extended by means of angular overlap calculations and ensuing correlation diagrams. A similar treatment has been made for complexes, such as those of Co and Rh . 5 39 jjjg photolysis rules, incidentally, are not as strongly obeyed with such complexes. 

The carbonato complexes undergo aquation to the corresponding aqua complexes by various paths depending on the nature of the complex. This aspect will be discussed briefly for complexes in which carbonate acts as a monodentate and bidentate ligand. The monodentate carbonato complexes of Co, Cr, Rh, and Ir, undergo acid-catalyzed decarboxylation. This can be represented by Eq. (28). 

A major factor in modeling hydroformylation reactions is that two gases (H2 and CO) are present compared to one gas (CO) in carbonylation. The most commonly used complexes are those of Co and Rh. A typical kinetic model for hydroformylation has the following hyperbolic (LHHW) form (Martin, 1954) ... 

A comparison of Co and Rh dioximato-complexes has been made for the aquation of /ra/w-[M(L)g(N02)Cl] (L=methylglyoximate, dmgH, or dioximate), and for the reverse (anation) reactions. The aquation rate increases as the electron-donating ability of L increases. Also, for trfl 5-[Co(L)2(S03)(am)] the rate of loss of am (am=py or NH3) varies with L in the order dmgH > methylglyoximate > diphenylglyoximate, and NH3 is lost more rapidly than py. ... 

The introduction of fluorine substituents instead of hydrogen may be a useful strategy for the synthesis of metalation-resistant NHCs. For example, vV-pentafluorophenylmethylene substituted NHC complexes of Ir and Rh showed no evidence of activation of C-H, C-C or C-F bonds. Grubbs and co-workers also prepared a NHC ligand designed to be resistant to orthome-talation by virtue of the presence of ortho fluorine substituents, and the metathesis catalysts prepared from these ligands displayed increased activity when compared to traditional IMes-based catalysts. ... 

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