New Carbenegold(I) Complexes Synthesized by the “Acac Method”

Synthesis and Chemistry of Ammonioethenyl and Phosphonioethenyl Ligands in Zwitterionic Dirhenium Carbonyl Complexes

New zwitterionic dirhenium carbonyl complexes containing ammonioethenyl and phosphonioethenyl ligands have been synthesized and studied. The reaction of Re₂(CO)₁₀ with C₂H₂ and Me₃NO yielded the dirhenium complex Re₂(CO)₉(NMe₃) (6) and the new zwitterionic complex Re₂(CO)₉[η¹-E-2-CH═CH(NMe₃)] (7). Compound 6 was characterized structurally and was found to have a NMe₃ ligand in an equatorial coordination site cis to a long Re-Re single bond, Re-Re = 3.0938(2) Å. Compound 7 can be obtained from the reaction of 6 with ethyne (C₂H₂) formally by the insertion of ethyne into the Re-N bond to the NMe₃ ligand. Compound 7 contains a 2-trimethylammonioethenyl ligand, ^-CH═CH(⁺NMe₃), that is formally a zwitterion having a positive charge on the nitrogen atom and a negative charge on the terminal carbon atom. When coordinated to rhenium by the terminal ethenyl carbon atom, the negative charge on the ^-CH═CH(⁺NMe₃) carbon atom is formally transferred to the rhenium atom. The reaction of Re₂(CO)₁₀ with C₂H₂ and NEt₃ in the presence of Me₃NO yielded the new dirhenium complex Re₂(CO)₉[η¹-E-2-CH═CH(NEt₃)] (8) together with some 6 and 7. Compound 8 is structurally similar to 7, but it contains a NEt₃ group in the ammonioethenyl ligand in the place of the NMe₃ group in 7. Reactions of 7 with PMePh₂ and PPh₃ yielded the zwitterionic 2-arylphosphonioethenyl-coordinated dirhenium carbonyl complexes, Re₂(CO)₉[η¹-E-2-CH═CH(PPh₂Me)] (9a) and Re₂(CO)₉[η¹-E-2-CH═CH(PPh₃)] (9b), and the zwitterionic 1-phosphonioethenyl ligand in the dirhenium carbonyl complexes, Re₂(CO)₉[η¹-1-C(PPh₂Me)(═CH₂)] (10a), Re₂(CO)₈[μ-η²-1-C(PPh₂Me)(═CH₂)] (11a), and Re₂(CO)₈[[μ-η²-1-C(PPh₃)(CH₂)] (11b). Compound 10a was converted to 11a and the new compound Re₂(CO)₇(μ-H)[μ-η²-1-(CH₂C)P(Ph)(Me)(o-C₆H₄)], (12) by decarbonylation using Me₃NO. Compound 12 contains an ortho-metalated phenyl ring. The new products 6,7, 8, 9b, 10a, 11a, 11b and 12 were characterized structurally by single-crystal X-ray diffraction analyses.

Synthesis, Structures, and Transformations of Bridging and Terminally-Coordinated Trimethylammonioalkenyl Ligands in Zwitterionic Pentaruthenium Carbido Carbonyl Complexes

Reactions of the pentaruthenium cluster complexes Ru₅(μ₅-C)(CO)₁₅ (5), Ru₅(μ₅-C)(CO)₁₄[μ-η²-O═C(NMe₂)](μ-H) (6), and Ru₅(μ₅-C)(CO)₁₅Cl(μ-H) (7) with ethyne (C₂H₂) in the presence of Me₃NO yielded the zwitterionic complexes Ru₅(μ₅-C)(CO)₁₃[μ-η²-CHCH(NMe₃)] (8), Ru₅(μ₅-C)(CO)₁₃[μ-η²-O═C(NMe₂)](η¹-E-CH═CH(NMe₃)(μ-H) (9), and Ru₅(μ₅-C)(CO)₁₃Cl[η¹-E-CH═CH(NMe₃)](μ-H) (11). Each product contains a positively charged trimethylammonioethenyl ligand, CH═CH(⁺NMe₃), that is derived from a 2-trimethylammonioethenide, ^-CH═CH(⁺NMe₃), zwitterion that formally has a positive charge on the nitrogen atom and a negative charge on the terminal enyl carbon atom. The trimethylammonioethenyl ligand, CH═CH(⁺NMe₃) in 8 is a η²-ligand that bridges a Ru-Ru bond on a basal edge of the square-pyramidal Ru₅ cluster by a combination of σ + π cooordination of the ethenyl group. Compounds 9 and 11 each contain a η¹-terminally coordinated [η¹-E-CH═CH(⁺NMe₃)] ligand with an E stereochemistry at the C═C double bond in open Ru₅ cluster complexes. Compound 9 was decarbonylated to yield the compound Ru₅(μ₅-C)(CO)₁₂[μ-η²-O═C(NMe₂)][μ-η²-CH═CH(NMe₃)](μ-H) (10) containing a η²-bridging CHCH(⁺NMe₃) ligand. Compound 10 was converted back to 9 by the addition of CO. Two zwitterionic products, Ru₅(μ₅-C)(CO)₁₄[η¹-E-CH═CH(NMe₃)] (12) and Ru₅(μ₅-C)(CO)₁₅[η¹-E-CH═CH(NMe₃)] (13), were obtained by the addition of CO to 8. Compound 12 is an intermediate en route to 13. Compound 12 contains a terminally coordinated η¹-E-CH═CH(⁺NMe₃) ligand on one of the basal Ru atoms of a square-pyramidal Ru₅ cluster. Compound 13 also contains a terminally coordinated η¹-E-CH═CH(⁺NMe₃) ligand on the wing-tip bridging Ru atom of a butterfly Ru₄C cluster. Treatment of 6 with methyl propiolate (HC≡CCO₂Me) yielded the zwitterionic complex Ru₅(μ₅-C)(CO)₁₃[μ-η²-O═C(NMe₂)][η¹-E-(MeO₂C)C═C(H)NMe₃](μ-H) (14) that is structurally similar to 9 but contains a η¹-E-(MeO₂C)C═C(H)(⁺NMe₃) ligand. Compound 14 eliminated the NMe₃ group to yield the compounds Ru₅(μ₅-C)(CO)₁₃[μ-η²-O═C(NMe₂)][μ-η²-(MeO₂C)HC═CH] (15) which contains a bridging methoxycarbonyl-substituted alkenyl ligand and the known compound Ru₅(μ₅-C)(CO)₁₃[μ-η²-O═C(NMe₂)](HNMe₂)(μ-H) (16).

Addition of N-nucleophiles to gold(iii)-bound isocyanides leading to short-lived gold(iii) acyclic diaminocarbene complexes

Addition of hydrazone to gold(iii)–isocyanides led to the generation of rare short-lived gold(iii) acyclic diaminocarbene complexes.

Carbene complexes of gold: preparation, medical application and bonding

New preparative methods for gold carbene complexes have been developed and older ones modified to prepare compounds with specific inherent properties for targeted applications. One of the important areas of application that has grown rapidly and wherein carbene complexes are increasingly significant falls within the field of medicine. Sophisticated theoretical calculations have accompanied many synthetic studies. These aspects are covered in this critical review (65 references).

Multinuclear Silver Ethynide Supramolecular Synthons for the Construction of Coordination Networks

The invariant appearance of the mu8 coordination mode for the C4(2-) dianion in its silver(I) complexes, with four silver(I) atoms attached to each terminal ethynide moiety, implies that the Ag4[cap]C[triple bond]C-C[triple bond]C[cap]Ag4 species may be considered as a new type of supramolecular synthon for the construction of 1D, 2D, and 3D coordination polymers. This Focus Review covers recent results on the synthesis and structural characterization of silver(I) arylethynide and alkylethynide complexes, which established the existence and utility of analogous polynuclear supramolecular synthons R-C[triple bond]C[cap]Ag(n) (R = aryl or alkyl; n = 4, 5) and Ag(n)[cap]C2-R-C2[cap]Ag(n) (R = p-, m-, o-C6H4; n = 4, 5). The interplay of silver-ethynide bonding, which can be classified into sigma, pi, and mixed (sigma,pi) types, with argentophilicity, pi-pi stacking, and other weak interactions highlights the complexity and challenge in building coordination networks of silver ethynide complexes.

Palladium Complexes of a Phosphorus Ylide with Two Stabilizing Groups: Synthesis, Structure, and DFT Study of the Bonding Modes

The phosphorus ylide ligand [Ph3P=C(CO2Me)C(=NPh)CO2Me] (L1) has been prepared and fully characterized by spectroscopic, crystallographic, and density functional theory (DFT) methods (B3LYP level). The reactivity of L1 toward several cationic Pd(II) and Pt(II) precursors, with two vacant coordination sites, has been studied. The reaction of [M(C/\X)(THF)2]ClO4 with L1 (1:1 molar ratio) gives [M(C/\X)(L1)]ClO4 [M = Pd, C/\X = C6H4CH2NMe2 (1), S-C6H4C(H)MeNMe2 (2), CH2-8-C9H6N (3), C6H4-2-NC5H4 (4), o-CH2C6H4P(o-tol)2 (6), eta3-C3H5 (7); M = Pt, C/\X = o-CH2C6H4P(o-tol)2 (5); M(C/\X) = Pd(C6F5)(SC4H8) (8), PdCl2 (9)]. In complexes 1-9, the ligand L1 bonds systematically to the metal center through the iminic N and the carbonyl O of the stabilizing CO2Me group, as is evident from the NMR data and from the X-ray structure of 3. Ligand L1 can also be orthopalladated by reaction with Pd(OAc)2 and LiCl, giving the dinuclear derivative [Pd(mu-Cl)(C6H4-2-PPh2=C(CO2Me)C(CO2Me)=NPh)]2 (10). The X-ray crystal structure of 10 is also reported. In none of the prepared complexes 1-10 was the C(alpha) atom found to be bonded to the metal center. DFT calculations and Bader analysis were performed on ylide L1 and complex 9 and its congeners in order to assess the preference of the six-membered N,O metallacycle over the four-membered C,N and five-membered C,O rings. The presence of two stabilizing groups at the ylidic C causes a reduction of its bonding capabilities. The increasing strength of the Pd-C, Pd-O, and Pd-N bonds along with other subtle effects are responsible for the relative stabilities of the different bonding modes.

Diaminocarbene- and Fischer-Carbene Complexes of Palladium and Nickel by Oxidative Insertion: Preparation, Structure, and Catalytic Activity

Oxidative insertion of [Pd(PPh3)4] or [Ni(cod)2]/PPh3 into the C-Cl bond of various 2-chloroimidazolinium- and other -amidinium salts affords metal-diaminocarbene complexes in good to excellent yields. This procedure is complementary to existing methodology in which the central metal does not change its oxidation state, and therefore allows to incorporate carbene fragments that are difficult to access otherwise. The preparation of a variety of achiral as well as enantiomerically pure, chiral metal-NHC complexes (NHC = N-heterocyclic carbene) and metal complexes with acyclic diaminocarbene ligands illustrates this aspect. Furthermore it is shown that oxidative insertion also paves a way to prototype Fischer carbenes of Pd(II). Since the required starting materials are readily available from urea- or thiourea derivatives, this novel approach allows for substantial structural variations of the ligand backbone. The catalytic performance of the resulting library of nickel- and palladium-carbene complexes has been evaluated by applications to prototype Suzuki-, Heck-, and Kumada-Corriu cross-coupling reactions as well as Buchwald-Hartwig aminations. It was found that even Fischer carbenes show appreciable catalytic activity. Moreover, representative examples of all types of neutral and cationic metal-carbene complexes formed in this study have been characterized by X-ray crystallography.