Transition metal boryl complexes

A catalytic cycle proposed for the metal-phosphine complexes involves the oxidative addition of borane to a low-valent metal yielding a boryl complex (35), the coordination of alkene to the vacant orbital of the metal or by displacing a phosphine ligand (35 —> 36) leads to the insertion of the double bond into the M-H bond (36 —> 37) and finally the reductive elimination to afford a hydroboration product (Scheme 1-11) [1]. A variety of transition metal-boryl complexes have been synthesized via oxidative addition of the B-H bond to low-valent metals to investigate their role in cat-... 

It is no coincidence that the first X-ray structure analysis of a transition metal-boryl complex [8] was made on the iridium complex jac-[IrH2(BC8Hi4)(PMe3)3] (2) [9] derived from the B—H activation of the 9-borabicyclo[3.3.1]-nonane (9-BBN)... 

Initial reports on the borylation of alkanes using isolated transition-metal-boryl complexes date back to 1995, when Hartwig showed that Cp Re(CO)2(Bpin)2 converts pentane to 1-borylpentane with high regioselectivity. " The catalytic C-H borylation of alkanes with Cp Re(CO)3 using photochemical activation was demonstrated soon thereafter (equation 25). Also, an efficient thermal process that involves the use of rhodium catalysts has since been developed (equation 26). It is interesting to note that this methodology is not restricted to small molecules, but has recently been exploited for the direct side-chain functionalization of polyolefins. ... 

Fig. 1 Principal orbital interactions for transition metal boryl complexes - a donor and 7i acceptor properties of the boryl ligand...

In this article emphasis has been placed on a review of crystallographic, spectroscopic and quantum chemical studies which shed light on the fundamental structure and bonding characteristics of the boryl ligand. The chemistry of transition-metal boryl complexes was reviewed extensively in 1998 [11,16-18], and a number of further review articles have been written in the interim [19-24]. Herein, we focus primarily on literature reports which have been published in the period 1998-2006, with due reference made to key systems reported in the pre-1998 period. The material includes three-... 

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