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Treatment of the complexes [Re(NO)2(PR3)2][BAr(F)4] (R = Cy, 1 a; R = iPr, 1 b) with phenyldiazomethane gave the cationic benzylidene species [Re{CH(C6H5)}(NO)2(PR3)2][BAr(F)4] (2 a and 2 b) in good yields. Upon reaction of 2 a and 2 b with acetonitrile, the consecutive formation of [Re(N[triple bond]CCH3)(N[triple bond]CPh)(NO)(OC(CH3)=NH)(PR3)][BAr(F)4] (3 a and 3 b) and [Re(NCCH3)(OC{CH3}NH{C6H5})(NO)(PR3)2][BAr(F)4] (4 a and 4 b) was observed. The proposed reaction sequence involves the coupling of coordinated NO, carbene and acetonitrile molecules to yield the (1Z)-N-[imino(phenyl)methyl]ethanimidate ligand. The coupling of the nitrosyl and the benzylidene is anticipated to occur first, forming an oximate species. The subsequent acetonitrile addition can be envisaged as a heteroene reaction of the oximate and the acetonitrile ligand yielding 3 a and 3 b, which in turn can cyclise and undergo a prototropic shift initiated by an internal attack of the ethaneimidate ligand on the benzonitrile moiety to afford 4 a and 4 b.

The addition of an excess of phenyldiazomethane to chlorobenzene solutions of the cationic dinitrosyl bisphosphine rhenium(-I) complexes [Re(NO)2(PR3)2][BAr(F)4] (R = Cy 1a, R = (i)Pr 1b) gave the corresponding benzylidene complexes [Re{=CH(C6H5)}(NO)2(PR3)2][BAr(F)4] (2a and 2b) in good yields. The treatment of 2b with dioxygen resulted in the oxidation of one of the nitrosyl ligands into the corresponding eta2-nitrito (3b) and nitrato complexes (4b) both in the solid state and in solution. In the case of the tricyclohexylphosphine derivative 2a the analogous conversion was not observed. A mechanism for the reaction of 2b with O2 is proposed which is based on an initial SET to the O2 molecule and subsequent formation of a peroxynitrite complex followed by the formation of a dinuclear mU-N2O4 intermediate. This in turn would undergo fission of the peroxo bond to afford 3b. A related sequence of steps is anticipated for the transformation of 3b to 4b. Furthermore, a similar mechanism seems reasonable for the seemingly topochemical reaction of 2b to 3b and 4b in the solid state. The initial SET to dioxygen and subsequent formation of the peroxynitrite complex is supported by DFT calculations on the trimethylphosphine model complexes [Re=CH{C6H5})(NO)2(PMe3)2]n+ (n = 1 and 2).

The asymmetric unit of the title compound, C(17)H(13)N(4)(+)center dot BF(4) , contains one half of the benzimidazolium cation and one half of the tetrafluoridoborate anion, with crystallographic mirror planes bisecting the molecules. One F atom of the tetrafluoridoborate is equally disordered about a crystallographic mirror plane. In the crystal, C-H center dot center dot center dot F interactions link the cations and anions into layers parallel to (100). The crystal packing is further stabilized by F center dot center dot center dot pi contacts involving the tetrafluoridoborate anions and the five-membered rings F center dot center dot center dot centroid = 2.811 (2) angstrom].

In the title paramagnetic 19-electron neutral complex, W(BH(4))(C(21)H(24)N(2))(2)(NO)(2)], the W(0) atom is coordinated by two 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) carbene ligands, two NO groups and two H atoms of an eta(2)-tetrahydroborate ligand. Depending on the number of coordination sites (n) assigned to the BH4(-) ligand, the coordination geometry of the W atom may either be described as approximately trigonal-bipyramidal (n = 1) or as very distorted octahedral with the bridging H atoms filling two coordination positions (n = 2). In the latter case, the coplanar NO groups and bridging H atoms (r.m.s. deviation = 0.032 angstrom) form one octahedral plane, with mutually trans-oriented carbene ligands. In the crystal, molecules are connected via C-H center dot center dot center dot O interactions.

In the crystal structure of the title compound, [WCl2(NO)(C6H16P2)2]Cl, the seven-coordinated tungsten(II) center displays a distorted pentagonal-bipyramidal geometry with trans nitrosyl and chloride ligands. The NO and Cl ligands are disordered over two positions; the site occupancy factors are 0.6 and 0.4.