Phosphine complexes carborane

With the relative air and water stability of silver phosphine complexes in mind, the Frost and Weller groups reported the use of a silver(I) carborane triphenylphosphine complex as a catalyst for the aza-Diels-Alder reaction.82,83 These unique catalyst complexes were able to catalyze the reaction of Danishefsky s diene (195) with 196 in... 

Other [AuCIL] complexes with monophosphines are those derived of o-carborane (427),2506 pyr-anoside group (428),2507 a-dimethylamino(3)ferrocenophan-2-yl,2508 calix[4]arene derived phosphites,25 or aminoxyl radical-substituted phosphines (429),2510 for which ferromagnetic interactions have been observed. 

Reaction of the mdo-carborane monoanion 7,8-C2B9Hi2 with phosphine-substituted transition metal complexes afforded novel hydridophosphino-mctallocarboranes (80) according to... 

The phosphine 1-(1,2-C2BxoHii)P(CHs)2 was prepared and reacted with an iridium (I) complex, as shown in Fig. 27. Spectroscopic evidence strongly supported the view that the complexed Ir(I) had inserted into a B—H bond with the formation of an iridium-boron bond and an iridium-hydride link (58). Specific deuterium labels attached to the carborane moiety of the phosphine clearly proved this point. Thus, the B-H vertices of the icosahedral carborane group that are nearest the carbon atom bearing phosphorus were shown to be involved, although a distinction could not be made between the 3,6 or 4,5 sets of BH groups. 

Ruthenium complexes bearing anionic carborane-phosphine and dicarbol-lide ligands. 

Although other transition metals have been found to catalyze hydroborations with HBcat, early studies have shown that rhodium complexes are the most effective for reactions of simple alkenes. The catalytic cycle proposed resembles one suggested previously for the rhodium-catalyzed addition of carborane B-H bonds to the C=C unit in acrylate esters. The reaction is believed to proceed via initial loss of phosphine and oxidative addition (see Oxidative Addition) of the B-H bond of HBcat to the coordinatively unsaturated (see Coordinative Saturation Unsaturation) rhodium center. Coordination ofthe alkene (seeAlkene Complexes) and subsequent insertion (see Insertion) into the Rh-H bond and reductive elimination (see Reductive Elimination) of the B-C bond then generates the organoboronate ester product(s) (Scheme 1). 

These complexes are isoelectronic and isostructural with the bis-phosphine Ir carbonyl chloride complex, but they differ in two respects (a) the reaction with is irreversible and (b) the oxidative addition of yields three different cis isomers as a result of a solvent dependence for this addition. The complexes trans-CPR ROjIrCCOftr-carb) (R = CjHj R = CgHj, CHj) react with or D, giving the (PR ROjIrH (or D ) (CO)((T-carb) dihydrides or dideuterides. These complexes are colorless crystalline compounds, nonelectrolytes in solution and stable with respect to thermal loss of either carborane or H, however, they are light sensitive. 

Ruthenium carborane complexes 1-8, were synthesized under argon using anhydrous solvents, according to procednres described in the literatnre (14-16). Coimnercial phosphines and diphosphines (Strem Chemicals) were nsed. The obtained prodncts were isolated and pnrified by colnnrn chromatography nsing silica gel Merck (230 00 mesh). 

Otiier reductive eliminations that form C-H bonds do occur after initial dissociation of a ligand. For example, the elimination of carborane in Equation 8.14, - the elimination of ketone in Equation 8.15, and the elimination of aldehyde in Equation 8.16 aU occur after dissociation of a phosphine ligand. In contrast, die reductive elimination of alkane from the zirconocene alkyl hydride complex in Equation 8.17 occurs after association of ligand. ... 

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