Synthesis, structure, and reactivity of beta-diketiminate boron(III) complexes

The chemistry of boron supported by the beta-diketiminate ligand, tolylnacn ac (tolylnacnacH=2-N-p-tolylamino-4-N-p-tolylimino-2-pentene), has been inv estigated. (tolylnacnac)Li reacted with one equivalent of BF3. OEt2 to affo rd (tolylnacnac)BF2 (1) in 46% yield. The structure of compound 1 was solve d indicating that the diketiminate ligand is eta(2)-bound to B to form a si x-membered heterocycle. While alkylation of compound 1 can be effected with alkyl lithium or Grignard reagents, nucleophilic addition to the diketimin ate ligand occurred in the reaction between compound 1 and MeLi to afford [ eta(2)-(Me)(2)C(Ntolyl)CH=C(Ntolyl)Me]BMe (2). For Me3SiCH2Li, deprotonatio n of the diketiminate ligand afforded [eta(2)-CH2=C(Ntolyl)CH=C(Ntolyl)Me]B CH2SiM3 (3). Conversely, alkyl Grignard reagents selectively delivered two alkyl groups to the boron center, and several pseudo-tetrahedral (tolylnacn ac)BR2 (4a-d; a, R=Me, b, R=Pr-n, c, R=vinyl, d, R=allyl) complexes have be en prepared. The structures of compounds 2, 3, and 4a were solved, and vari ations in B-N and B-C metrical data for compounds 2 and 4a were correlated to bond order, inductive effects of the co-ligands, and hybridization of th e boron center. The reaction between compound 4a and tris(pentafluoraphenyl )boron gave [(tolylnacnac)BMe](+)[MeB(C6F5)](-) (5). Compound 5 reacted wit h pyridine to give an adduct, [(tolylnacnac)B(py)Me](+)[MeB(C6F5)(3)](-) (6 ). (C) 1999 Elsevier Science Ltd. All rights reserved.