Mono-, di-, and triborylphosphine analogues of triarylphosphines

Diazaborinylphosphines based on the 1,8-diaminonaphthylboronamide heterocycle are prepared by a chlorosilane-elimination reaction, and their structural and bonding properties are compared to those of PPh3. The precursor chloroborane ClB{1,8-(NH)2C10H6} (I) is fully characterized including its crystal structure, which features intermolecular π-π stacking, B···N interactions, and N-H···Cl hydrogen bonding. Treatment of I with Ph3-nP(SiMe3)n gave the corresponding Ph3-nP(B{1,8-(NH)2C10H6})n, {L1 (n = 1), L2 (n = 2), and L3 (n = 3)}. The crystal structures of L1-3 reveal an increase in the planarity at P as a function of n, and the steric bulk of the diazaborinyl substituent B{1,8-(NH)2C10H6} is similar to that of a phenyl. Nucleus-independent chemical shift calculations were carried out that suggest that the 14 π-electron diazaborinyl substituent can be described as aromatic overall, though the BN2-containing ring is slightly antiaromatic. The complexes cis-[Mo(L1-3)2(CO)4] (1-3) are prepared from [Mo(nbd)(CO)4] (nbd = norbornadiene) and L1-3. From the position of the ν(CO) (A1) band in the IR spectra of 1-3, it is deduced that the diazaborinyl substituent has a donating capacity similar to an alkyl group.