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The reactions of the 16-electron cycloheptatrienyl−cyclopentadienyl−zirconium sandwich complex [(η7-C7H7)Zr(η5-C5H5)] (1) with tert-butyl isocyanide (tBuNC) and 2,6-dimethylphenyl isocyanide (o-XyNC) have been studied. The isocyanide complexes [(η7-C7H7)(η5-C5H5)Zr(CNR)] (R = tBu, 2a; R = o-Xy, 2b) can be isolated in quantitative yield as stable orange (2a) or red (2b) crystalline solids. The CN stretching vibrations are observed at 2156 (2a) and 2134 cm-1 (2b) in KBr, indicating a relatively weak zirconium−isocyanide interaction. Solution NMR studies consequently reveal that the isocyanides quickly exchange on the NMR time scale at room temperature. The equilibrium reaction of 1 with tBuNC has been examined in further detail by dynamic NMR spectroscopy, allowing an enthalpy for the formation of 2a of ΔH° = −39.6 ± 6.6 kJ mol-1 to be established. DFT calculations reveal that the weakness of the zirconium−isocyanide bonds in 2a and 2b can be attributed to the strong and appreciably covalent zirconium−cyclo...

A theoretical study has been carried out on two types of olefin polymerization catalysts based on the same M(III) centers (M = Ti, V, Cr) but different (mono) anionic ligand designs. The first system contains a mono-β-diiminato ligand that binds through the two imine nitrogens to the M(III) center and has the nitrogen lone-pairs perpendicular to the NMN coordination plane. It is shown that the generic mono-β-diiminato ligand system without bulky substituents on the nitrogen has barriers (kcal/mol) for insertion (Ti: 10.7; V: 12.2; Cr: 10.4) quite similar to the β-hydrogen transfer process (BHT) (Ti: 11.2; V: 9.8; Cr: 8.4), which serves as the chain-terminating step. The close proximity of the two barriers is in line with findings for other bidentate nitrogen ligands, where bulky aryl groups on the nitrogens were required in order to increase the BHT barrier relative to insertion and ensure acceptable molecular weights. The second system contains a bridged diamide ligand in which the ligand backbone ...

We present an investigation on the potential of first-row transition metals with a d-electron count from 1 to 4 as olefin polymerization catalysts by means of first-principles density functional theory (DFT) type calculations. We considered generic model systems [MLL‘R]+ with M = Ti, V, Cr, and Mn (R = Me, Et) in high-spin electron configuration bearing two nitrogen ligands L,L‘ (NH2- and NH3) in order to elucidate the effect of partially filled d-levels on the elementary steps of ethylene polymerization. The olefin uptake energy is found to diminish almost linearly with an increasing number of d-electrons due to a successive destabilization of the metal acceptor orbital. Ethylene insertion barriers were calculated to be between 6 and 16 kcal/mol (R = Et) and are less affected by the d-electron count than by the type of the transition metal and its oxidation state. The dominant termination process for most systems is a β-hydrogen transfer (BHT) to the monomer. Its barrier follows the trends of the olefin ...

Quantum-mechanical calculations based on density functional theory (DFT) have been carried out on the migratory insertion process [M(CO)2I3(CH3)]- → [M(CO)I3(COCH3)]- (M = Rh, Ir), which represents...

Hydroformylation regioselectivities of rhodium−phosphine ligand systems are calculated according to a perspicuous formula that connects the regioselectivity of one phosphine coordination mode to th...

The equilibrium structures of rhodium complexes HRh(CO)n(PR3)4-n and HRh(CO)n(PR3)3-n with n = 1−3 and R = H have been calculated using density functional theory (DFT) with both local and gradient-corrected functionals. These molecules are model systems for the analogous complexes with R = alkyl or aryl involved in homogeneously catalyzed hydroformylation, the largest scale organometallic catalysis known to date. For the compounds with n = 1 and n = 2, ab initio calculations at the HF and MP2 level of theory have been performed as well. Basis sets of valence double-ζ plus polarization quality were used, and in the case of the ab initio calculations effective core potentials for rhodium and phosphorus were applied. The ligand dissociation energies derived from single-point CCSD(T) calculations revealed that MP2 strongly overestimates bond strengths for these systems. The DFT calculations using gradient-corrected functionals yielded values very close to the CCSD(T) energies. Comparison with experimental res...

The geometry and electronic structure of borylferrocenes, FcBR2, have been investigated by X-ray structure analysis (R = Br) and density functional theory (DFT) calculations (R = H). An interaction...

By example of the bidentate phosphine−phosphite ligand BINAPHOS 1, [(2-diphenylphosphino)-1,1‘-binaphthalen-2‘-yl)(1,1‘-binaphthalen-2,2‘-diyl)phosphite], a semiquantitative theoretical model eluci...