1H and 13C NMR studies of η6-benzo-bonded (boron-nitrogen heteroarene)tricarbonylchromium complexes and related η6-phenyl-bonded (B, B', B''-trimethyl-N, N', N''-triarylborazine)-tricarbonylchromium complexes: crystallographic structure of a boron-nitrogen heteroarene

Article abstract of DOI:10.1016/0022-328X(94)80079-0

2,4-dimethyl-3-phenyl-<2'-methyl-3'-chloro>-7-chloro-8-methyl-2,4-dibora-1,3-diazaronaphthalene (C16H18B2N2Cl2) crystallizes in the monoclinic system: P_2/a; a=8.149(3) Angstroem, b=13.379(3) Angstroem and c=15.193(3) Angstroem; β=91.03(2)^o; Z=4; R=0.043; R_w=0.041.Reaction with gives exclusively the compounds with Cr(CO)3 η⁶-bonded to the benzo part of the molecule.This derivative is a 1:1 mixture of atropisomers which were partially separated and whose configurations could be deduced by means of solvent effects in nuclear magnetic resonance (NMR) spectroscopy.Similar results were obtained with 2,4-dimethyl-3-phenyl-<2'-methyl-4'-chloro>-6-chloro-8-methyl-2,4-dibora-1,3-diazaronaphthalene and although the separation of isomers failed.Additionally, two closely related η⁶-bonded isomers originating from the above ligands were identified in which the chlorine atom was replaced by a hydrogen atom.All these compounds were thoroughly characterized by high resolution 1H and 13C one-dimensional and 1H-1H nuclear Overhauser spectroscopy (NOESY) and correlated two-dimensional NMR spectroscopy (COSY).Further, the reaction of with B,B',B''-trimethyl-N,N',N''-triarylborazine, the phenyl bearing a para substituent (H, F or Me), was shown by 1H and 13C NMR spectroscopy to yield a compound with one phenyl group η⁶ bonded to Cr(CO)3.Key words: Chromium; Boron; Nuclear magnetic resonance