Methyl and ethyl cyanide react with diborane and form borine adducts of the type RCN,BH,, which dissociate reversibly a t low temperatures. They decompose a t ca. 20" and O", respectively, to form N'N"N"'-triethyl-and N'N"N"'-tri-n-propyl-borazole. Evidence is presented for the intermediate formation of a compound of the type (R=CH=N*BH,),. Preliminary experiments show that similar but less stable borine adducts are formed by vinyl and phenyl cyanide. Diborane also reacts with cyanogen and hydrogen cyanide, but these products were not characterised.LITTLE information is available on the reaction of diborane with volatile cyanides. Schlesinger and Burg reported the formation of a solid adduct MeCN,BH, from diborane and methyl cyanide. Its dissociation at room temperature into the gaseous reactants was accompanied by slight decomposition to an involatile liquid, which was not identified. Burg2 suggests that two hydrogen atoms shift from boron to the carbon of the cyanide group forming an N-substituted borazole, but gives no supporting evidence. Preliminary experiments on the reaction of diborane with acrylonitrile have also shown that a mixture of unidentified involatile products is formed., Silyl cyanide also reacts with diborane, forming initially an adduct similar to that with methyl cyanide. When heated, however, monosilane is lost, leaving a polymer (BH,CN),.*The experiments described in this paper were made to determine the nature of the decomposition products from the methyl cyanide adduct and also to find if similar adducts are formed by other cyanides. The formation of the compound MeCN,BH, was confirmed and, from measurements of its dissociation pressure (-34" to 4O) a heat of dissociation of the solid complex into methyl cyanide and diborane of 11.2 kcal. mole-l was deduced. This may be compared with the value of 31.3 kcal. mole-l for the dissociation of solid trimethylamine-borine, Me,N,BH, into gaseous trimethylamine and d i b ~r a n e . ~ Using Bauer's value of 28 kcal. molew1 for the heat of dissociation of diborane into borine radicals, the heat of dissociation of MeCN,BH, into gaseous MeCN and BH, is 25 kcal. moleL1. Comparable values for other methyl cyanide adducts are: MeCN,BF,, 26-5 kcal. mole-l; MeCN,BCl,, 33.4 kcal. mole-l (ref.
7).The infrared spectrum of the adduct showed bands at 3000, 2940, 2280, 1445, 1414, 1366, 1030, and 913 cm.-l which, after allowance for small shifts, are common to methyl cyanides and the adduct. The chief additional bands were at 2400-2340 cm.-l (B-H stretch) and 1160-1 140 (asymmetrical BH, deformation). The position of absorption bands due to the B-N stretch vibration is not certain. Bands in the region 1250-980 cm.-l have been assigned to this vibration in boron-nitrogen addition compounds by various author^,^ although Taylor and Cluff ,lo who studied the spectra of deuterated derivatives of ammonia-borine, H,N,BH,, concluded that the B-N band appears in the region 750-650 cm.-l.The solid adduct decomposed in a few days at 20" to a colourless liquid from which