Heterobimetallic complexes of the formulations (NHC)Cu−FeCp(CO) 2 (NHC = IPr, IMes, SIMes), (IPr)Cu− MoCp(CO) 3 , and (IPr)(Cl)Zn−FeCp(CO) 2 were synthesized in high yield from readily available starting materials and characterized crystallographically. The solid-state structures of the Cu−Fe systems reveal close, secondary interactions between Cu and one CO ligand from the [FeCp(CO) 2 ] unit that are absent in the Zn−Fe analogue. The heterobimetallic complexes feature short yet polar Cu−Fe, Cu−Mo, and Zn−Fe bonds in which the electrophilic metal (Cu, Zn) is later in the transition series than the nucleophilic metal (Fe, Mo), thereby subverting the more common early−late heterobimetallic paradigm. DFT analyses were used to assess M−M′ bond polarity and examine effects on M−M′ bonding of systematic modifications to both the nucleophilic and electrophilic fragments. Experimental confirmation of Cu−Fe bond polarity was obtained by analysis of product mixtures resulting from the reactions between (NHC)Cu−FeCp(CO) 2 complexes and MeI, which produced (NHC)Cu−I and Me−FeCp(CO) 2 products.

The five-coordinate iron(II) hydride complex ( iPr PNP)Fe(H)CO ( iPr PNP = N[CH 2 CH 2 (P i Pr 2 )] 2 ) was found to selectively catalyze deaminative hydrogenation of amides to the corresponding amines and primary alcohols. It is one of the most active amide hydrogenation catalysts reported to date, with turnover numbers (TONs) in excess of 1000 observed for multiple substrates and TONs greater than 4000 obtained for activated formanilides. The amide C−N cleavage reactions occur with a preference for electron-withdrawing substituents and with greater activity for formamides compared with acetamides and benzamides. Stoichiometric reactions between ( iPr PNP)Fe(H)CO and formanilide afforded the new iron(II) complex ( iPr PN H P)Fe(H)CO(N(Ph)HCO) resulting from N−H addition across the Fe−N bond. Complexes of this type were identified as the resting state during catalytic hydrogenation reactions containing secondary amides. Addition of a Lewis acid cocatalyst provided further enhancement of the productivity of catalytic amide hydrogenations.

Building upon the precedent of catalytically active (NHC)Cu-FeCp(CO)2 complexes, a series of (NHC)Cu-[M] complexes were synthesized via the addition of Na(+)[M](-) reagents to (NHC)CuCl synthons. The different [M](-) anions used span a range of 7 × 10(7) relative nucleophilicity units, allowing for controlled variation of nucleophile/electrophile pairing in the heterobimetallic species. Direct Cu-M bonds (M = Cr, Mn, Co, Mo, Ru, W) formed readily when the bulky IPr carbene was used as a support. Crystallographic characterization and computational examination of these complexes was conducted. For the smaller IMes carbene, structural isomerism was observed when using the weakest [M](-) nucleophiles, with (IMes)Cu-[M] and {(IMes)2Cu}{Cu[M]2} isomers being observed in equilibrium. Collectively, the series of complexes provides a toolbox for catalytic reaction discovery with precise control of structure-function relationships.

A family of iron(II) carbonyl hydride species supported by PNP pincer ligands was identified as highly productive catalysts for the N-formylation of amines via CO 2 hydrogenation. Specifically, iron complexes supported by two different types of PNP ligands were examined for formamide production. Complexes containing a PNP ligand with a tertiary amine afforded superior turnover numbers in comparison to complexes containing a bifunctional PNP ligand with a secondary amine, indicating that bifunctional motifs are not required for catalysis. Systems incorporating a tertiary amine containing a PNP ligand were active for the N-formylation of a variety of amine substrates, achieving TONs up to 8900 and conversions as high as 92%. Mechanistic experiments suggest that N-formylation occurs via an initial, reversible reduction of CO 2 to ammonium formate followed by dehydration to produce formamide. Several intermediates relevant to this reaction pathway, as well as ironcontaining deactivation species, were isolated and characterized.

A new, high yield synthesis of [Ni(S(2)C(2)Me(2))(2)] (3) is described using 4,5-dimethyl-1,3-dithiol-2-one, Me(2)C(2)S(2)CO (1), as dithiolene ligand precursor. Reaction of (Me(2)C(2)S(2))Sn(n)Bu(2), 2, with WCl(6) produces tris(dithiolene) [W(S(2)C(2)Me(2))(3)] (6) and demonstrates the potential synthetic utility of this compound in metallodithiolene synthesis. The series of compounds [W(S(2)C(2)Me(2))(x)(CO)(6-2x)] (x = 1-3), obtained as a mixture via the reaction of [Ni(S(2)C(2)Me(2))(2)] with [W(MeCN)(3)(CO)(3)], has been characterized structurally. A trigonal prismatic geometry is observed for [W(S(2)C(2)Me(2))(CO)(4)] (4) and confirmed by a DFT geometry optimization to be lower in energy than an octahedron by 5.1 kcal/mol. The tris(dithiolene) compound [W(S(2)C(2)Me(2))(3)] crystallizes in disordered fashion upon a 2-fold axis in C2/c, a different space group than that observed for its molybdenum homologue (P1), which is attributed to a slightly smaller chelate fold angle, alpha, in the former. The reactivity of 4 and [W(S(2)C(2)Me(2))(2)(CO)(2)] (5) toward PMe(3) has been examined. Compound 4 yields only [W(S(2)C(2)Me(2))(CO)(2)(PMe(3))(2)] (7), while 5 produces either [W(S(2)C(2)Me(2))(2)(CO)(PMe(3))] (8) or [W(S(2)C(2)Me(2))(2)(PMe(3))(2)] (9) depending upon reaction conditions. Crystallographic characterization of 5, 8, and 9 reveals a trend toward greater reduction of the dithiolene ligand (i.e., more ene-1,2-dithiolate character) across the series, as manifested by C-C and C-S bond lengths. These structural data indicate a profound effect exerted by the pi-acidic CO ligands upon the apparent state of reduction of the dithiolene ligand in compounds with ostensibly the same oxidation state.