Structural-functional analogue of the reduced site of dissimilatory nitrate reductase is synthesized as [Et4N][MoIV(SPh)(PPh3)(mnt)2].CH2Cl2 (1). PPh3 in 1 is readily dissociated in solution to generate the active site of the reduced site of dissimilatory nitrate reductase. This readily reacts with nitrate. The nitrate reducing system is characterized by substrate saturation kinetics. Oxotransfer to and from substrate has been coupled to produce a catalytic system, NO3- + PPh3 --> NO2- + OPPh3, where NO3- is the substrate for dissimilatory nitrate reductase. The corresponding chloro complex, [Et4N][MoIV(Cl)(PPh3)(mnt)2].CH2Cl2 (2), responds to similar PPh3 dissociation but is unable to react with nitrate, showing the indispensable role of thiolate coordination for such oxotransfer reaction. This investigation provides the initial demonstration of the ligand specificity in a model system similar to single point mutation involving site directed mutagenesis in this class of molybdoenzymes.

The argentate trinuclear cluster Ag3(μ2-3,5-(CF3)2PyrPy)3 (3,5-(CF3)2PyrPy = 2,2′-pyridylpyrrolide– ligand) catalytically promotes the insertion of the carbene of ethyl diazoacetate at room temperature into the C–H bond of a series of alkanes ranging from ethane to hexane, as well as branched and cyclic hydrocarbons. In addition to experimental studies, we also present theoretical studies elucidating the mechanism to C–H activation and functionalization by the transient silver carbene monomer (3,5-(CF3)2PyrPy)Ag(CHCO2Et). On the basis of DFT studies, formation of the silver carbene complex was found to be rate-determining for alkane substrates such as ethane and propane. On the other hand, DFT studies on methane, a substrate that we failed to activate, revealed that carbene insertion into the C–H bond was overall rate-determining. Theoretical analysis of charge flow also shows that the change from separated reagents to the TS involves charge flow from alkane to the silver carbene carbon with the bridging H behaving as a conduit. KIE studies using cyclohexane as a substrate suggest that the product-determining step involves only modest C–H bond lengthening, which can be also represented as a very early transition state with respect to C–H insertion of the carbene.

In the presence of stoichiometric or catalytic amounts of [M{N(SiMe3)2}2] (M=Fe, Co), N‐heterocyclic carbenes (NHCs) react with primary phosphines to give a series of carbene phosphinidenes of the type (NHC)⋅PAr. The formation of (IMe4)⋅PMes (Mes=mesityl) is also catalyzed by the phosphinidene‐bridged complex [(IMe4)2Fe(μ‐PMes)]2, which provides evidence for metal‐catalyzed phosphinidene transfer.

Two synthetic protocols, a salt metathesis reaction and a direct metalation, were developed for preparing 1,4diaza-1,3-butadiene complexes of barium, strontium, and calcium, in which 1,4-diaza-1,3-butadiene serves as a dianionic or monoanionic ligand. A salt metathesis reaction of BaI 2 with the dipotassium salt of N,N′-bis(2,6-diisopropylphenyl)-1,4-diaza-1,3butadiene (1; abbreviated (Dip) 2 DAD) afforded the iodide-bridged dinuclear complex [[K((Dip) 2 DAD)(THF) 2 ][Ba(μ-I)(THF) 2 ]] 2 (2) bearing a dianionic ene-diamide ligand, while the reaction of MI 2 (M = Sr, Ca) with the dipotassium salt of 1 gave the mononuclear complexes [M((Dip) 2 DAD)[THF] 4 ] (4, M = Sr; 5, M = Ca). A direct metalation reaction of barium powder with (Dip) 2 DAD in the presence of iodine (10 mol%) afforded an iodide-bridged dinuclear complex, [Ba((Dip) 2 DAD)(μ-I)(THF) 2 ] 2 (3), in which (Dip) 2 DAD coordinates as a monoanionic ligand to the barium center, as was evident from the X-ray analysis and the EPR spectral data. The products from the direct metalation reaction of Sr and Ca powders with 1 in the presence of a catalytic amount of iodine (1 mol%) resulted in the formation of mononuclear complexes 4 and 5 bearing the dianionic ene-diamide DAD ligand.

Dedicated to Professor F. Ekkehardt Hahn on the occasion of his 65th birthday Heterobimetallic complexes bearing NHC donor ligands are gaining immense popularity in organometallic chemistry and tandem catalysis. It is known that the NHC reacts with Pd II in the presence of pyridine to yield PEPPSI type complexes and the NHC ligands having ortho-CÀ H proton easily orthometalate to Ir III or Rh III centers. Combining these two methodologies in a stepwise fashion, we present here a series of heterobimetallic Ir III À Pd II and Rh III À Pd II complexes from a dicarbene donor ligand featuring cyclometalated Ir III or Rh III and mixed NHC^Py/PPh 3 coordinated Pd II centers. All the heterobimetallic complexes have been structurally characterized by X-ray crystallographic analysis. The heterobimetallic complexes featuring mixed NHC^PPh 3 coordinated Pd II centers show better activity in tandem Suzuki-Miyaura/transfer hydrogenation reactions compared to both, the heterobimetallic complexes possessing PEPPSI type Pd II centers, and the equimolar mixture of their mononuclear Pd II and Rh III or Ir III counterparts. The heterobimetallic complex featuring cyclometalated Ir III and mixed NHC^PPh 3 coordinated Pd II center shows excellent selectivity for 4-biphenylmethanol (isolated yield: 92 %) in tandem catalysis.