K. Oguro

Alkoxycarbene complexes of nickel(II)

Abstract Alkynylnickel complexes trans-C6Cl5Ni(PPhMe2)2CCR (IIIa, R  H; IIIb, R  Me; IIIc, R  Et; IIId, R  CH2OH; IIIe, R  CH2CH2OH; IIIf, R  Ph; IIIg, R  C6H4OMe-p) have been prepared from trans-[C6Cl5Ni-(PPhMe2)2L]ClO4 and monosubstituted acetylenes in the presence of triethylamine, and their reactions with alcohols in the presence of perchloric acid were studied. Complexes IIIa and IIIe afforded alkoxycarbene complexes trans-[C6Cl5Ni-(PPhMe2)2{C(OR′)Me}]ClO4 (IVa, R′  Me; IVb, R′  Et; IVc, R′  n-Pr) or trans-C6Cl5Ni(PPhMe2)2{ C(CH 2 ) 3 O }]ClO4(IVd), respectively, but IIIb either decomposed or afforded trans-C6Cl5Ni(PPhMe2)2CHC(OMe)Me, depending on the amount of acid used. Treatment of IVaIVd with amines resulted in deprotonation to give α-alkoxyvinyl complexes, trans-C6Cl5Ni(PPhMe2)2C(OR′)CH2 (VIaVIc) or trans-C6Cl5Ni(PPhMe2)2 CCHCH 2 CH 2 O (VId), the reaction being reversible. A 1H NMR study indicated: (i) that the carbene methyl and the vinyl protons IV or VI are D-exchangeable by MeOD without catalyst; (ii) that the basicity of VIa is comparable to those of amines; (iii) that the carbene complexes IVaIVc have two isomers due to hindered rotation about the C(carbene)O bond in solution, IVb existing in the Z-form in the solid state; (iv) that the rotationalbarriers (°G≠) about the C(carbene)O bond in IVb and the NiC-(carbene) bond in IVd are 20 (or more) and 11.7 kcal/mol, respectively. These results are explained in term of double bond character of the carbene carbon and its surrounding atoms.

Cationic and alkynyl complexes of the trans(mesityl)bis(phenyldimethylphosphine)nickel(II) moiety

Abstract A cationic complex, trans-[(mesityl)Ni(PPhMe2)2(NCMe)]ClO4 (IIa), has been prepared rom trans-(mesityl)Ni(PPhMe2)2Br and silver perchlorate in acetone/acetonitrile. IIa reacts with several neutral ligands to give trans-[(mesityl)Ni(PPhMe2)2L]ClO4 (L = 2-pic, 3-pic, 3,4-lut, 2,5-lut, methyl isonicotinate, N-ethyl imidazole, PPhMe2, P(Ome)3), with halide anions to give trans-(mesityl)Ni(PPhMe2)2X (X = Cl, NNN), and with terminal alkynes in the presence of triethylamine to give trans-(mesityl)Ni(PPhMe2)2CCR (R = H, Me, CH2CH2Oh, Ph, C6H4OMe-p). Some related alkynyl complexes trans-CCl2CClNi(PPhMe2)2CCR (R = H, Me, Ph, C6H4OMe-p) and trans-{(o-MeO)2C6H3}Ni(PPhMe2)2CCr (R = H, Ph) also have been prepared from the corresponding trans-R′Ni(PPhMe2)2Cl, silver perchlorate and HCCR in acetonitrile-triethylamine. trans-(Mesityl)Ni(PPhMe2)2CCH reacts with methanol in the presence of perchloric acid to give a cationic carbne complex, trans-[(mesityl)Ni(PPhMe2)2{C(OMe)Me}]ClO4.

Organonickel(III) complexes

Abstract Paramagnetic organonickel(III) complexes, RNi(PPhMe2)2Br2 (R = CCl2=CCl or C6Cl5), have been prepared by the reaction of trans-RNi(PPhMe2)2Br with N-bromosuccinimide.

Reactions of some diorganonickel(II) complexes with N-bromosuccinimide

The reactions of some diorganonickel(II) complexes with N-bromosuccinimide (NBS) resulted in facile bromine for hydrogen substitution in aromatic, alkynyl or alkenyl substituents, or in the addition of NBS to CC bonds.

Cationic carbene complexes of nickel(II)

The nickel acetylide (1) reacts with alcohols in the presence of perchloric acid to give stable cationic alkoxy-carbene complexes (2), the 1H n.m.r. spectra of which show the presence of two conformational isomers; deprotonation with triethylamine occurs at the carbene methyl group.