Well-defined four-coordinate iron(II) complexes for intramolecular hydroamination of primary aliphatic alkenylamines.

Despite the growing interest in iron catalysis and hydroamination reactions, iron-catalyzed hydroamination of unprotected primary aliphatic amines and unactivated alkenes has not been reported to date. Herein, a novel well-defined four-coordinate ß-diketiminatoiron(II) alkyl complex is shown to be an excellent precatalyst for the highly selective cyclohydroamination of primary aliphatic alkenylamines at mild temperatures (70-90 °C). Both empirical kinetic analyses and the reactivity of an isolated iron(II) amidoalkene dimer, [LFe(NHCH2 CPh2 CH2 CHCH2 )]2 favor a stepwise σ-insertive mechanism that entails migratory insertion of the pendant alkene into an iron-amido bond associated with a rate-determining aminolysis step.

C-H bond activation of benzene by unsaturated η2-cyclopropene and η2-benzyne complexes of niobium.

We report the synthesis of a niobium cyclopropyl complex, Tp(Me2)NbMe(c-C(3)H(5))(MeCCMe), and show that thermal loss of methane from this compound generates an intermediate that is capable of activating both aliphatic and aromatic C-H bonds. Isotopic labeling, trapping studies, a detailed kinetic analysis, and density functional theory all suggest that the active intermediate is an η(2)-cyclopropene complex formed via ß-hydrogen abstraction rather than an isomeric cyclopropylidene species. C-H activation chemistry of this type represents a rather unusual reactivity pattern for η(2)-alkene complexes but is favored in this case by the strain in the C(3) ring which prevents the decomposition of the key intermediate via loss of cyclopropene.

2-Indenylidene pincer complexes of zirconium and palladium.

[IndH(2)(Ph(2)P=X)(2)] derivatives (1, X = NMes; 4, X = S) react with [Zr(NMe(2))(4)] and [PdCl(2)(cod)] to afford the complexes {[Ind(Ph(2)PNMes)(2)]Zr(NMe(2))(2)} (3), {[Ind(Ph(2)PS)(2)]Zr(NMe(2))(2)} (5), and {[Ind(Ph(2)PS)(2)]Pd(HNc-Hex(2))} (7). The ability of the phosphazene and thiophosphinoyl side arms to support the coordination of the indenyl ring as 2-indenylidene was evidenced by NMR spectroscopy and X-ray diffraction studies. Analysis of the bonding situation by density functional theory calculations revealed a strong sigma interaction but a negligible (if any) pi interaction between C2 and the metal.

C-H bond activation of arenes by a transient eta2-cyclopropene niobium complex.

The intermolecular C-H bond activation of benzene occurs under very mild conditions (room temperature) via a rare stereospecific 1,3-H addition on an unsaturated eta2-cyclopropene intermediate generated by a beta-H abstraction of CH4 from TpMe2NbMe(c-C3H5)(MeCCMe) to give TpMe2NbPh(c-C3H5)(MeCCMe).

Structure and bonding in a cyclobutyl tris(pyrazolyl)boratoniobium complex and the variation in agostic behaviour with ring size in the series Tp(Me2)NbCl(c-C(n)H(2n-1))(MeC[triple bond]CMe), n = 3-6.

The synthesis and characterisation of the cyclobutyl complex Tp(Me2)NbCl(c-C4H7)(MeC[triple bond]CMe) completes the family of cycloalkyl complexes Tp(Me2)NbCl(c-C(n)H(2n-1)), n = 3-6. The properties of the cyclobutyl complex are qualitatively similar to those of its cyclopentyl and cyclohexyl analogues, and dramatically different from those of the cyclopropyl derivative. Most conspicuously, the cyclobutyl system has an alpha-C-H agostic interaction in the dominant isomer, with no evidence for the alpha-C-C agostic character found for the smaller ring. C-C agostic character therefore seems to be unique to the cyclopropyl complex, where the acute C-C-C angles destabilise the C-C bonding orbitals.