131545-45-4Relevant academic research and scientific papers
Synthesis and structure of diarylboryl-substituted hydrazines and diphosphanes: Role of σ-orbital hybridization and π-orbital overlap in N-N and P-P multiple-bond lengths
Pestana, Doris C.,Power, Philip P.
, p. 528 - 535 (2008/10/08)
The synthesis and spectroscopic and structural characterization of several substituted diphosphanes and hydrazines have been carried out in order to estimate the relative importance of rehybridization and π-bonding in N-N and P-P double-bond lengths. The presence of the -BMes2 (Mes = 2,4,6-Me3C6H2) group in the compounds Mes2B(1-Ad)PPPh2 (1) (1-Ad = 1-adamantyl), [Mes2B(1-Ad)P]2 (2), and [Mes2B(Mes)P]2 (3) induces essential planarity at the boryl-substituted phosphorus atoms and dramatic changes in the P-P bond lengths. Normally, single P-P bonds are about 2.22 A? long, as is observed in [Mes(I)P]2 (4), whereas in 1 the P-P bond length is near 2.17 A? and in 2 and 3 it is near 2.11 A?. The latter distance is about halfway between those of normal single and double P-P bonds. The use of the -BMeS2 group as a substituent on hydrazines also results in planarity at the boryl-substituted nitrogen and in the shortening of the N-N bonds. In this case, however, the percentage change in the N-N bond length is not as great as that seen in the phosphorus compounds. For example, the N-N bond length in Mes2B(Ph)NN(H)Ph (5) is near 1.44 A? and in Mes2B(H)NN(H)BMes2 (6) it is 1.41 A? whereas in hydrazine the N-N distance is 1.46 A? (cf. N-N double bond ≈ 1.25 A?). Oddly, the N-N bond length in 1,2-diphenylhydrazine (7) is 1.39 A?. In this case, however, the nitrogen is almost planar and the N-C bond is short. The larger changes observed in the diphosphanes have been interpreted on the basis of the relative weakness of the P-P π-bond and the fact that the hybridization changes in phosphorus are significantly greater than those observed for nitrogen. Similarly, comparison of the data for 1-7 with the normal bond lengths for P-P and N-N double bonds, which are 2.02 and 1.25 A? long, respectively, leads to the conclusion that p-p π-bonds account for only about half of the shortening in P-P double bonds whereas they account for ～70-75% of the contraction in the case of N-N double bonds.
