Boranes carbonylation

In Scheme 13.8, the side chain was added in one step by a borane carbonylation reaction. This synthesis is very short and the first four steps were used to transform the aldehyde group in the starting material to a methyl ester. The stereochemistry at C(4)-C(7) is established in the hydroboration in Step B, in which the C(7)-H bond is formed. A 1 1 mixture of diastereomers resulted, indicating that the configuration at C(4) has little influence on the direction of approach of the borane reagent. 

Ni catalysts for olefin polymerization incorporating a-iminocarboxamide ligands are activated by the formation of borane-carbonyl adducts (153).542 Structure/reactivity relationships are similar to Brookhart s dimine catalysts. 

Carbonyls of some Main Group metals have been detected under matrix isolation conditions, e.g., Alx(CO)2 (42), Gax(CO)2 (91), and Sn(CO) (n = 1-3 ) (87). Bonding in these compounds is presumably of the soft-acid-soft-base class as in borane carbonyl, with only a minimal contribution from 7r-bonding. 

Borane carbonyl BHjCO Borazine B3N3H Boron tribromide BBr Boron trichloride BClj Boron trifluoride BF Bromodiborane BjHsBr Diborane(6) B2H... 

This salt is a stable, crystalline solid at room temperature. Borane-carbonyl is regenerated by treating the carbonate analog with poly-phosphoric acid 46>. 

Coordinative adducts of lower stability are formed by nontransition elements or by transition elements with empty reacts with CO at 90°C, equilibrium is rapidly attained and borane carbonyl is formed. ... 

L. T. Redmon, G. D. Purvis, III, and R. J. Bartlett, /. Am. Chem. Soc., 101, 2856 (1979). Accurate Binding Energies of Diborane, Borane Carbonyl, and Borazane Determined by Many-Body Perturbation Theory. (Correlated polarization exponents for DZP basis sets.)... 

The compound borane-carbonyl occupies a special position in any discussion of molecules derived from boron hydrides with boron-carbon bonds. Carbon monoxide reacts with diborane (20 atm/room temperature) to give an adduct of the borane group which does not rearrange or lose hydrogen (39) The adduct OC BH3 does, however, dissociate into carbon monoxide and diborane at ordinary temperatures. No carbonyls of other Group III acceptor molecules have been prepared so far 133), and it has been suggested 27, 58) that borane-carbonyl owes its existence to the ability of the hydrogen atoms of borane to transfer electrons to a vacant p,-orbital in carbon monoxide. 

Diborane is not unique among the boron hydrides in its ability to form a carbonyl. High pressure reaction of either pentaborane-f / or tetra-borane-10 with carbon monoxide forms a substance which behaves like borane-carbonyl in its manner of decomposition. The formula of this polyborane-carbonyl has recently been established as OC B Hg (mp, — 114.5° bp, 59.6°) 41a). It reacts with trimethylamine without release of carbon monoxide. 

The diammoniate of borane carbonyl was first prepared by BURG and SCHLESINGER in 1937(1). Using chemical and spectroscopic methods CARTER and PARRY (2) showed that the closely related bis-methylamine adduct of borane carbonyl is a methyl ammonium salt of a new N-methyl borano-carbamate anion ... 

The corresponding value for bicarbonate is 4,7.10" With SS H PO potassium boranocarbonate liberates borane carbonyl in excellent yield in dilute acid solution hydrolysis of the liberated borane carbonyl occurs. 

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