We present a comparison of experiment and theory of ultrafast one-color pump–probe multiphoton ionization spectrocopy of K2. The wave packet propagation in the A 1Σu+ state and in the (2) 1Πg Rydberg state is monitored in detail by changing systematically the pump and probe wavelength from 779 nm to 837 nm. The measured total ionization rates as a function of the delay time between pump and probe are shown to depend sensitively on the pump and probe wavelengths used and exhibit drastic changes and a variety of fascinating structures as the direct observation of inward and outward wave packet detection and frequency doubling of the detected wave packet oscillation. The time dependent quantum mechanical wave packet calculations are in excellent agreement with the experimental results and allow a clear interpretation of different ionization pathways and mechanisms observed in the femtosecond ion signal.

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.

Bis(di-tert-butylphosphany1)methane Complexes of Rhodium: Geometry, Electronic Structure, and Derivatives of the 14-Electron Fragment [Rh(dtbpm)Cl]. Molecular Structure of Rh(dtbpm)Cl (PMe,) 14-Electron fragments [M(PR,),X] (M = Rh, Ir, X = halogen etc.) are considered to be an important class of highly reactive, coordinatively unsaturated intermediates in many metal-induced stoichiometric or catalytic transformations of organic substrates. As available theoretical data suggest a slightly preferred T-shaped groundstate geometry with a less symmetric cis rather than the usually implied trans phosphane arrangement for such tricoordinate d'-ML3-type systems with monodentate phosphanes PR3, the chemistry of q2-diphosphanylmethane complexes of rhodium with four-membered RhPCPchelate rings and thus with enforced cis phosphane coordination and anomalously small cis P -Rh -P angles has been studied by theory and by experiment. MO calculations (EH) have been performed both for the model 14-electron system (Rh(dhpm)Cl] (dhpm = diphosphanylmethane, H2P -CH2 -PH2) and for the experimentally accessible fragment [Rh(dtbpm)Cl], where dtbpm is bis(di-tert-butylphosphany1)-methane, (~B U )~P -CH2-P(tBu)2. The electronic and geometric structure of these species is described. Employing the unusual ligand dtbpm, tailor-made for stabilizing mononuclear $-and destabilizing dinuclear p-diphosphanylmethane coordination, the chloro-bridged dimer [Rh(dtbpm)Clj,, has been synthesized. In agreement with steric and electronic considerations, its chemistry is dominated by a facile dissociation to monomeric (presumably solvent coordinated) fragments [Rh(dtbpm)Cl], even in benzene, as suggested by molecular mass determinations. Accordingly, by using [Rh(dtbpm)Cljz as a starting material, a series of sterically very congested but nevertheless mononuclear, square-planar complexes Rh(dtbpm)Cl(L) (L = CO, PMe3, PPh3, PCy,, pyridine, acrylonitrile) with chelating dtbpm could be readily prepared and fully characterized. The relative stability of these potential alternative precursors of a [Rh(dtbpm)Cl] intermediate towards dissociation of ligands L is reported. The molecular structure of Rh(dtbpm)C1(PMe3) as the first representative of this class of compounds has been determined by X-ray crystallography.

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