γ‐C−H agostic stabilization of the 14‐electron metal center by a saturated hydrocarbon group characterizes the structure of the first neutral, three‐coordinate alkylrhodium(I) complex [(κ2‐dtbpm)RhNp] (1; dtbpm = bis(di‐tert‐butylphosphanyl)methane, Np=neopentyl). Some of its reactions, for example, N2 complexation and C−H bond activation, are reported.

Chiral, enantiopure aggregates are formed spontaneously by mixing solutions of n-butyllithium with anisyl fenchols. X-ray crystal analyses reveal the structures of these aggregates with different ortho substituents in the anisyl moieties (X), X = H (1-H), SiMe3 (2-H), tBu (3-H) SiMe2(tBu) (4-H) and Me (5-H). While the complex of 1-BuLi shows a 3:1 composition, 2-BuLi, 3-BuLi and 4-BuLi yield 2:2 stoichiometries. The aggregate 5-BuLi crystallizes with a 2:4 composition and hence is a derivative of hexameric n-butyllithium, in which two trans-situated nBuLi molecules are substituted by lithium fencholate moieties. The variety in the synthesized chiral nBuLi aggregates demonstrates the high propensity of anisyl fencholates to chirally modify nBuLi. Variations in the modular ligand structures by alterations of the ortho-substituents (X) enable tunings of compositions and also of enantioselectivities in nBuLi additions to benzaldehyde.

Modeling the chemistry of ketene complex {κ 2 -(t-Bu) 2 PCH 2 P(t-Bu) 2 }IrCl[η 2 -(C,C)-Ph 2 Cd CdO] (1), DFT studies have been carried out for (, and for their interconversion by intramolecular CdC double bond cleavage/formation. A qualitative MO analysis from extended Hu ¨ckel calculations shows the CdC cleavage and formation to be symmetry allowed at a d 8 -ML 2 late transition metal template. For the two iridium model complexes B and C the process is calculated by DFT to be reversible, with activation barriers of 17.3 kcal mol -1 toward the more stable carbonyl carbene system and 25.1 kcal mol -1 for the reverse reaction, respectively. This is in line with experimental observations for 1, which generates {κ 2 -(t-Bu) 2 PCH 2 P(t-Bu) 2 }Ir(CPh 2 )-(CO) + (3) upon chloride abstraction and regenerates 1 after the addition of chloride. QM/ MM calculations of the ONIOM type have been employed for the real systems 1 and 3, to take into account and to evaluate the role of steric effects and to allow a validation of theoretical results by comparing computed and X-ray-determined structures. Contrasting the iridium case, the analogous rhodium ketene complex (is computed to be favored by 8.0 kcal mol -1 compared to its carbene carbonyl isomer (κ 2 -H 2 PCH 2 PH 2 )Rh(CH 2 )(CO) + (H), with a barrier of 22.9 kcal mol -1 for the endothermic CdC cleavage step. Conceivable dynamic processes were treated theoretically for the temperature dependence of NMR line shapes of carbene complex {κ 2 -(t-Bu) 2 PCH 2 P-(t-Bu) 2 }Ir(CPh 2 )(CO) + (3). A comparison with the experimental data suggests a plausible pathway for the observed exchange of the two P centers.

The reaction of the γ-agostic 14 VE complex [(κ2-dtbpm)Rh(Np)] (1) with olefins opened an access to neutral, cis-alkyl olefin complexes (κ2-dtbpm)Rh(Np)(η2-olefin) (2a/b, Np = neopentyl, olefin = ethylene, methylacrylate) bearing the cis chelating bisphosphine ligand dtbpm (bis(di-tert-butylphosphino)methane, t Bu2P-CH2-P t Bu2). They represent the first structurally characterized examples of neutral Rh systems with cis bisphosphine ligation, isoelectronic to the presumed resting states in late transition metal (e.g., Pd, Ni) catalyzed polymerization reactions. Their solid-state molecular structures revealed an unexpected, non-square-planar coordination mode of the olefin moiety, with the center of the CC double bond moved 34° out of the P2RhCNp plane. In solution rapid dynamic processes interconvert equivalent structures with the olefin above or below this plane. DFT and QM/MM (ONIOM) calculations reproduce correctly the minimum geometries found in the crystal structures. They are caused by electronic effects, as shown by fragment MO (NBO analysis) and frontier MO arguments. The unusual structure motif carries over to the chloro complexes (κ2-dtbpm)Rh(Cl)(η2-olefin) (5a/b, olefin = fumaronitrile, acrylonitrile). No polymerization is observed when 2a is exposed to an excess of ethylene, indicating a rather high olefin insertion barrier for this uncharged RhI species, in agreement with DFT calculations of the transition state for ethylene insertion into the Rh−CNp bond of (κ2-dhpm)Rh(Np)(η2-C2H4) (2a*). This contrasts with the high catalytic activity of isolectronic NiII and PdII systems.