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The cyanoborate process on limonene [Eq. (e)], successful with the~ylborane,[~] essentially failed for mesitylborane. This might be due to the greater facility of thexylborane, as compared to mesitylborane, for the hydroboration of more hindered alkenes. It defines at least one area in which thexylborane will retain an advantage over mesitylborane.2.NaCN; TFAA; H20, I NaOH A We next examined the displacement of the mesityl group from dialkylmesitylboranes, and found two unusual and highly selective processes that further enhance the usage of mesitylborane. The first method consisted of the addition of bromine in methanol to the dialkylmesitylboranes [Eq. (f)] . This caused cleavage of the mesityl group with production of bromomesitylene and dialkylmethoxyboranes, oxidation of which gave the corresponding alcohols in overall yields of 82-87%.More importantly, the intermediate dialkylmethoxyboranes can be reacted directly with a Grignard reagent to give fully mixed organoboranes, in which all the alkyl groups can be primary. These in turn can be readily converted to the corresponding tertiary alcohols ['11 [Eq. (g)]. When R' = n-octyl, RZ = nhexyl, R3 = n-butyl, the overall yield of isolated carbinol, based on MesBH, is 69%, which implies a highly efficient process given the seven steps involved.

The chelating trisphenol ligands tris(2-hydroxyphenyl)amine (1H 3 ) and tris(2-hydroxy-4,6-dimethylbenzyl)amine (2H 3 ) proved to be excellent precursors for the chelating phenoxides, and the latter has been used to prepare a series of cyclopentadienylmetal derivatives of early transition metals. For niobium and tantalum, reactions with CpMCl 4 lead to the compounds CpMCl(1) and CpMCl( 2). An X-ray diffraction study of CpNbCl(1) establishes a pseudo-octahedral structure with a trans disposition of the η 5 -cyclopentadienyl ring and the nitrogen atom of the chelating ligand. Similar reactions of CpTiCl 3 lead to the CpTi(1) and CpTi(2) analogues. Electrochemical experiments provide useful information on the reduction potentials of the compounds, from which it is clear that ligand 2 is a stronger donor than is 1. At the same time, it appears that chelate ring size is important; while the reduction of complexes containing 1 are largely reversible, those of complexes containing 2 are irreversible. This is interpreted to mean that the six-membered rings in the latter are opening during reduction, a process involving formal loss of an aryloxide from the metal center. In an attempt to correlate this solution reactivity with catalytic efficiency in a bond-forming process, the compounds were screened for activity as styrene polymerization catalysts in the presence of methylaluminoxane cocatalyst. While the niobium and tantalum analogues were inactive, the titanium compounds of 1 showed high activity and appreciable selectivity for the preparation of syndiotactic polystyrene.(1) (a) Wesleyan University. (b) Yale University.(2) (a) Bradley, D. C.

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