A synthesis has been developed that allows the isolation of four-coordinate [(tpy)Ni-Br] (1, tpy = terpyridine) in high yield. Complex 1 has been structurally characterized, and the X-ray data reveal a square-planar geometry, unlike the known [(tpy')Ni-I] (tpy' = 4,4',4''-tri-tert-butyl-terpyridine) but similar to [(tpy)Ni-CH(3)]. In the solid-state, EPR spectroscopy indicates, however, that unlike [(tpy)Ni-CH(3)], the electronic structure of 1 is a metal-centered, not a ligand-centered radical. Density functional theory (DFT) analyses support this assignment. The preparation of 1 also facilitated the analysis of the redox potentials of a series of terpyridine nickel derivatives. It was found that the overall ligand sphere (one vs two coordinated terpyridine ligands) plays more of a role in determining the redox potentials of these derivatives than do the formal oxidation states of the nickel ions in the solution phase.

Alkynes are rapidly hydroaminated by primary amines using titanium dipyrrolylmethane derivatives as catalyst.

The readily prepared pyrrolyl complex Ti(NMe2)2(dpma), where dpma is di(pyrrolyl-α-methyl)methylamine, is an effective precatalyst for the hydroamination of alkynes by primary amines. The catalysis is Markovnikov-selective and rapid with terminal alkynes.

Syntheses and properties of group-4 complexes incorporating the tridentate, dianionic ligand N,N-(dipyrrolyl-alpha-methyl)-N-methylamine, dpma, have been investigated. Addition of 1 equiv of H(2)dpma to Ti(NMe(2))(4) and Zr(NMe(2))(4) results in transamination with 2 dimethylamides providing Ti(NMe(2))(2)(dpma) and Zr(NMe(2))(2)(NHMe(2))(dpma), respectively. Addition of 2 equiv of H(2)dpma to Zr(NMe(2))(4) and Hf(NMe(2))(4) results in production of the homoleptic complexes Zr(dpma)(2) and Hf(dpma)(2). Conversely, treatment of Ti(NMe(2))(4) with 2 equiv of H(2)dpma does not provide Ti(dpma)(2), which was available by addition of 2 Li(2)dpma to TiCl(4). The properties of the isostructural series M(dpma)(2) were investigated by single crystal X-ray diffraction, cyclic voltammetry, (14)N NMR, and other techniques. By (14)N NMR, it was found that the pyrrolyl resonance chemical shift changes approximately linearly with the electronegativity of the metal center, which was attributed to pi-interaction between the pyrrolyl nitrogen lone pair and the metal. Other complexes produced during this study include Ti(CH(2)SiMe(3))(NMe(2))(dpma), TiCl(2)(THF)(dpma), and Ti(OCH(2)CF(3))(2)(THF)(dpma). Two isomers for Ti(CH(2)SiMe(3))(NMe(2))(dpma) were isolated and characterized.

Treatment of M(NAr) 2 (Cl) 2 (DME), where Ar ) 2,6-diisopropylphenyl, with cyclooctyne results in the formation of M(dC 8 H 12 dC 8 H 12 dNAr)(Cl) 2 (NAr), where M ) Mo (1) and W (2). The complexes have metrical and spectroscopic parameters that are most consistent with an alkylidene-imine formulation with some participation by the alkyl-amido resonance form. Thermolysis of metallacycles 1 and 2 generates a pyrrole elimination product, with the tungsten derivative being more thermally stable. In addition, the metallacycle is quite hydrolytically stable. Addition of 50% H 2 SO 4 to a toluene solution of 2 protolytically cleaves all the ligands on the metal except those associated with the metallacycle, which are retained in the oxo product [W(O)(µ-O)(d C 8 H 12 dC 8 H 12 dNAr)] 2 (3). The metallacycles 1-3 will polymerize norbornene in the presence of AlCl 3 . Compounds 1-3 and the pyrrole were characterized by X-ray diffraction.