H-1 AND C-13 NMR-STUDIES OF ETA-6-BENZO-BONDED (BORON-NITROGEN HETEROARENE) TRICARBONYLCHROMIUM COMPLEXES AND RELATED ETA-6-PHENYL-BONDED (B,B',B''-TRIMETHYL-N,N',N''-TRIARYLBORAZINE)-TRICARBONYLCHROMIUM COMPLEXES - CRYSTALLOGRAPHIC STRUCTURE OF A BORON-NITROGEN HETEROARENE

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: P2/a; a = 8.149(3) angstrom, and b = 13.379(3) angstrom and c = 15.193(3) angstrom; beta = 91.03(2)-degree; Z = 4; R = 0.043; R(w) = 0.041. Reaction with [Cr(CO)6] gives exclusively the compounds with Cr(CO)3 eta6-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 [Cr(CO)6] although the separation of isomers failed. Additionally, two closely related eta6-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 H-1 and C-13 one-dimensional and H-1-H-1 nuclear Overhauser spectroscopy (NOESY) and correlated two-dimensional NMR spectroscopy (COSY). Further, the reaction of [Cr(CO)6] with B,B',B''-trimethyl-N,N',N''-triarylborazine, the phenyl bearing a para substituent (H, F or Me), was shown by H-1 and C-13 NMR spectroscopy to yield a compound with one phenyl group eta6 bonded to Cr(CO)3.