Synthesis and Study of Cationic,Two‐Coordinate Triphenylphosphine– Gold–π Complexes

Cationic, two‐coordinate triphenylphosphine–gold(I)–π complexes of the form [(PPh₃)Au(π ligand)]⁺ SbF₆^? (π ligand=4‐methylstyrene, 1? SbF₆), 2‐methyl‐2‐butene ( 3? SbF₆), 3‐hexyne ( 6? SbF₆), 1,3‐cyclohexadiene ( 7? SbF₆), 3‐methyl‐1,2‐butadiene ( 8? SbF₆), and 1,7‐diphenyl‐3,4‐heptadiene ( 10? SbF₆) were generated in situ from reaction of [(PPh₃)AuCl], AgSbF₆, and π ligand at ?78 °C and were characterized by low‐temperature, multinuclear NMR spectroscopy without isolation. The π ligands of these complexes were both weakly bound and kinetically labile and underwent facile intermolecular exchange with free ligand (ΔG^≠≈9 kcal mol^?1 in the case of 6? SbF₆) and competitive displacement by weak σ donors, such as trifluoromethane sulfonate. Triphenylphosphine–gold(I)–π complexes were thermally unstable and decomposed above ?20 °C to form the bis(triphenylphosphine) gold cation [(PPh₃)₂Au]⁺SbF₆^? ( 2? SbF₆).     

Group 11 complexes containing the [C5(CN)5]- ligand; 'coordination-analogues' of molecular organometallic systems

The reactions of Na[C(5)(CN)(5)] (Na[1]) with group 11 phosphine complexes [(P)(n)MCl] (M = Cu, Ag, Au, P = Ph(3)P; M = Cu, P = dppe (Ph(2)PCH(2)CH(2)PPh(2))] give a range of compounds containing the pentacyanocyclopentadienide ligand, [C(5)(CN)(5)](-) (1). The new complexes [(Ph(3)P)(2)M{1}](2) [M = Cu (3); M = Ag (5)], [(Ph(3)P)(3)Ag{1}] (4), [(dppe)(3)Cu(2){1}(2)] (6) and [Au(PPh(3))(2)][1] (7) include the first complete series of group 11 complexes of any cyclopentadienide ligand to be structurally characterised.     

Cationic NHC-gold(I) complexes: Synthesis, isolation, and catalytic activity

The reaction of [(NHC)AuCl] complexes (NHC = N-heterocyclic carbene) with a chloride abstractor of the type AgX, where X is a non-coordinating anion, led, in the presence of a neutral coordinating solvent S, to a series of cationic gold(I) complexes of formulae [(NHC)Au(S)]X. Hence, different cationic NHC-gold(I) species bound to acetonitrile, pyridine, 2-Br-pyridine, 3-Br-pyridine, norbornadiene, and THF could be synthesized and characterized by ¹H and ¹³C NMR spectroscopies. Among these, the results of X-ray diffraction studies for [(IPr)Au(NCMe)]SbF₆, [(IAd)Au(NCMe)]PF₆, [(IPr)Au(pyr)]PF₆, [(IPr)Au(2-Br-pyr)]PF₆, [(IPr)Au(3-Br-pyr)]PF₆ are discussed. As special feature, the structure of [(IPr)Au(2-Br-pyr)]PF₆ presented a secondary interaction between the gold and bromine atoms. Additionally, while attempting to obtain crystals of [(IPr)Au(nbd)]PF₆, we crystallized a decomposition product featuring a very rare anion as bridging ligand with formulae [(μ-PF₄)((IPr)Au)₂]PF₄. The observation of a possible P-F bond activation has important implications for cationic Au-based homogeneous catalysis. Finally, we compared the catalytic activities of the different cationic [(NHC)Au(S)]X complexes in the allylic acetate rearrangement reaction and notably observed the inertness of pyridine-based catalysts.     

{Au(IPr)}2(μ-OH)]X complexes: synthetic, structural and catalytic studies

The synthesis of a series of dinuclear gold hydroxide complexes has been achieved. These complexes of type [{Au(IPr)}₂(μ‐OH)]X (X=BF₄, NTf₂, OTf, FABA, SbF₆; IPr=2,6‐bis(disopropylphenyl)imidazol‐2‐ylidene; NTf₂=bis(trifluoromethanesulfonyl)imidate; OTf=trifluoromethanesulfonate; FABA=tetrakis(pentafluorophenyl)borate) are easily formed in the presence of water and prove highly efficient in the catalytic hydration of nitriles. Their facile formation in aqueous media suggests they are of relevance in gold‐catalyzed reactions involving water. Additionally, a series of [Au(IPr)(NCR)][BF₄] (R=alkyl, aryl) complexes was synthesized as they possibly occur as intermediates in the catalytic reaction mechanism. ¹H and ¹³C NMR data as well as key bond lengths obtained by X‐ray diffraction studies are compared and reveal an interesting structure–activity relationship. The collected data indicate a negligible effect of the nature of the nitrile on the reactivity of [Au(L)(NCR)][X] complexes in catalysis.     

Stable ‐ESiMe3 Complexes of CuI and AgI (E=S,Se) with NHCs: Synthons in Ternary Nanocluster Assembly

As a part of efforts to prepare new “metallachalcogenolate” precursors and develop their chemistry for the formation of ternary mixed‐metal chalcogenide nanoclusters, two sets of thermally stable, N‐heterocyclic carbene metal–chalcogenolate complexes of the general formula [(IPr)Ag?ESiMe₃] (IPr=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene; E=S, 1 ; Se, 2 ) and [(iPr₂‐bimy)Cu?ESiMe₃]₂ (iPr₂‐bimy=1,3‐diisopropylbenzimidazolin‐2‐ylidene; E=S, 4 ; Se, 5 ) are reported. These are prepared from the reaction between the corresponding carbene metal acetate, [(IPr)AgOAc] and [(iPr‐bimy)CuOAc] respectively, and E(SiMe₃)₂ at low temperature. The reaction of [(IPr)Ag?ESiMe₃] 1 with mercury(II) acetate affords the heterometallic complex [{(IPr)AgS}₂Hg] 3 containing two (IPr)Ag?S^? fragments bonded to a central Hg^II, representing a mixed mercury–silver sulfide complex. The reaction of [(iPr₂‐bimy)Cu‐SSiMe₃]₂, which contains a smaller N‐heterocyclic‐carbene, with mercuric(II) acetate affords the high nuclearity cluster, [(iPr₂‐bimy)₆Cu₁₀S₈Hg₃] 6 . The new N‐heterocyclic carbene metal–chalcogenolate complexes 1 , 2 , 4 , 5 and the ternary mixed‐metal chalcogenolate complex 3 and cluster 6 have been characterized by multinuclear NMR spectroscopy (¹H and ¹³C), elemental analysis and single‐crystal X‐ray diffraction.     

First Evidence for the Existence of Hexafluoroantimonic(V) Acid

By reacting IPr ? InBr₃ with AgSbF₆ in dichloroethane at room temperature, we could obtain single crystals comprising [{(IPr ? InBr₃)(Ag ? (CH₂Cl)₂)}₂][SbF₆]₂ ( 1 ) and two identical HSbF₆ units. It is presumed that the reaction gave rise to [IPr ? InBr_3?x][SbF₆]_x (x=1, 2, or 3) which reacted with adventitious water to give HSbF₆ and [IPr ? InBr_3?x(OH)][SbF₆]_x?1. The experiment was reproduced at 60 °C, eventually leading to the indium hydroxide [{IPr ? In(OH)_0.5(H₂O)_4.5}₂][SbF₆]₅ ( 2 ).     

N‐Heterocyclic Carbene–Phosphinidyne Transition Metal Complexes

The N‐heterocyclic carbene–phosphinidene adduct IPr?PSiMe₃ is introduced as a synthon for the preparation of terminal carbene–phosphinidyne transition metal complexes of the type [(IPr?P)ML_n] (ML_n=(η⁶‐p‐cymene)RuCl) and (η⁵‐C₅Me₅)RhCl). Their spectroscopic and structural characteristics, namely low‐field ³¹P NMR chemical shifts and short metal–phosphorus bonds, show their similarity with arylphosphinidene complexes. The formally mononegative IPr?P ligand is also capable of bridging two or three metal atoms as demonstrated by the preparation of bi‐ and trimetallic RuAu, RhAu, Rh₂, and Rh₂Au complexes.     

Expanded‐Ring N‐Heterocyclic Carbenes for the Stabilization of Highly Electrophilic Gold(I) Cations

Strategies for the synthesis of highly electrophilic Au^I complexes from either hydride‐ or chloride‐containing precursors have been investigated by employing sterically encumbered Dipp‐substituted expanded‐ring NHCs (Dipp=2,6‐iPr₂C₆H₃). Thus, complexes of the type (NHC)AuH have been synthesised (for NHC=6‐Dipp or 7‐Dipp) and shown to feature significantly more electron‐rich hydrides than those based on ancillary imidazolylidene donors. This finding is consistent with the stronger σ‐donor character of these NHCs, and allows for protonation of the hydride ligand. Such chemistry leads to the loss of dihydrogen and to the trapping of the [(NHC)Au]⁺ fragment within a dinuclear gold cation containing a bridging hydride. Activation of the hydride ligand in (NHC)AuH by B(C₆F₅)₃, by contrast, generates a species (at low temperatures) featuring a [HB(C₆F₅)₃]^? fragment with spectroscopic signatures similar to the “free” borate anion. Subsequent rearrangement involves B?C bond cleavage and aryl transfer to the carbophilic metal centre. Under halide abstraction conditions utilizing Na[BAr^f₄] (Ar^f=C₆H₃(CF₃)₂‐3,5), systems of the type [(NHC)AuCl] (NHC=6‐Dipp or 7‐Dipp) generate dinuclear complexes [{(NHC)Au}₂(μ‐Cl)]⁺ that are still electrophilic enough at gold to induce aryl abstraction from the [BAr^f₄]^? counterion.     

Three-Coordinate Rhodium Complexes in Low Oxidation States

The isolation of simultaneously low-coordinate and low-valent compounds is a timeless challenge for preparative chemists. This work showcases the preparation and full characterization of tri-coordinate rhodium(-I) and rhodium(0) complexes as well as a rare rhodium(I) complex. Reduction of [{Rh(μ-Cl)(IPr)(dvtms)}₂] ( 1 , IPr=1,3-bis(2,6-diisopropylphenyl)imidazolyl-2-ylidene; dvtms=divinyltetramethyldisiloxane) with KC₈ gave the trigonal complexes K[Rh(IPr)(dvtms)] and [Rh(IPr)(dvtms)], whereas the cation [Rh(IPr)(dvtms)]⁺ results from their oxidation or by abstraction of chloride from 1 with silver salts. The paramagnetic Rh⁰ complex is a unique fully metal-centered radical with the unpaired electron in the d_z2 orbital. The Rh(-I) complex reacts with PPh₃ with replacement of the NHC ligand, and behaves as a nucleophile, which upon reaction with [AuCl(PPh₃)] generates the trigonal pyramidal complex [(IPr)(dvtms)Rh-Au(PPh₃)] with a metal–metal bond between two d¹⁰ metal centers.     

Triptycene‐Based Chiral and meso‐N‐Heterocyclic Carbene Ligands and Metal Complexes

Based on 1‐amino‐4‐hydroxy‐triptycene, new saturated and unsaturated triptycene‐NHC (N‐heterocyclic carbene) ligands were synthesized from glyoxal‐derived diimines. The respective carbenes were converted into metal complexes [(NHC)MX] (M=Cu, Ag, Au; X=Cl, Br) and [(NHC)MCl(cod)] (M=Rh, Ir; cod=1,5‐cyclooctadiene) in good yields. The new azolium salts and metal complexes suffer from limited solubility in common organic solvents. Consequently, the introduction of solubilizing groups (such as 2‐ethylhexyl or 1‐hexyl by O‐alkylation) is essential to render the complexes soluble. The triptycene unit infers special steric properties onto the metal complexes that enable the steric shielding of selected areas close to the metal center. Next, chiral and meso‐triptycene based N‐heterocyclic carbene ligands were prepared. The key step in the synthesis of the chiral ligand is the Buchwald–Hartwig amination of 1‐bromo‐4‐butoxy‐triptycene with (1S,2S)‐1,2‐diphenyl‐1,2‐diaminoethane, followed by cyclization to the azolinium salt with HC(OEt)₃. The analogous reaction with meso‐1,2‐diphenyl‐1,2‐diaminoethane provides the respective meso‐azolinium salt. Both the chiral and meso‐azolinium salts were converted into metal complexes including [(NHC)AuCl], [(NHC)RhCl(cod)], [(NHC)IrCl(cod)], and [(NHC)PdCl(allyl)]. An in situ prepared chiral copper complex was tested in the enantioselective borylation of α,β‐unsaturated esters and found to give an excellent enantiomeric ratio (er close to 90:10).     

Efficient Rhodium‐Catalyzed Multicomponent Reaction for the Synthesis of Novel Propargylamines

[{Rh(μ‐Cl)(H)₂(IPr)}₂] (IPr = 1,3‐bis‐(2,6‐diisopropylphenyl)imidazole‐2‐ylidene) was found to be an efficient catalyst for the synthesis of novel propargylamines by a one‐pot three‐component reaction between primary arylamines, aliphatic aldehydes, and triisopropylsilylacetylene. This methodology offers an efficient synthetic pathway for the preparation of secondary propargylamines derived from aliphatic aldehydes. The reactivity of [{Rh(μ‐Cl)(H)₂(IPr)}₂] with amines and aldehydes was studied, leading to the identification of complexes [RhCl(CO)IPr(MesNH₂)] (MesNH₂ = 2,4,6‐trimethylaniline) and [RhCl(CO)₂IPr]. The latter shows a very low catalytic activity while the former brought about reaction rates similar to those obtained with [{Rh(μ‐Cl)(H)₂(IPr)}₂]. Besides, complex [RhCl(CO)IPr(MesNH₂)] reacts with an excess of amine and aldehyde to give [RhCl(CO)IPr{MesN?CHCH₂CH(CH₃)₂}], which was postulated as the active species. A mechanism that clarifies the scarcely studied catalytic cycle of A₃‐coupling reactions is proposed based on reactivity studies and DFT calculations.     

Diaminogermylene and diaminostannylene derivatives of gold(I): novel AuM and AuM2 (M = Ge, Sn) complexes

The reactions of [AuCl(THT)] (THT = tetrahydrothiophene) with 1 equiv of the group 14 diaminometalenes M(HMDS)(2) [M = Ge, Sn; HMDS = N(SiMe(3))(2)] lead to [Au{MCl(HMDS)(2)}(THT)] [M = Ge (1), Sn (2)], which contain a metalate(II) ligand that arises from insertion of the corresponding M(HMDS)(2) reagent into the Au-Cl bond of the gold(I) reagent. While compound 1 reacts with more Ge(HMDS)(2) to give the germanate-germylene derivative [Au{GeCl(HMDS)(2)}{Ge(HMDS)(2)}] (3), which results from substitution of Ge(HMDS)(2) for the THT ligand of 1, an analogous treatment of compound 2 with Sn(HMDS)(2) gives the stannate-stannylene derivative [Au{SnCl(HMDS)(2)}{Sn(HMDS)(2)(THT)}] (4), which has a THT ligand attached to the stannylene tin atom and which, in solution at room temperature, participates in a dynamic process that makes its two Sn(HMDS)(2) fragments equivalent (on the NMR time scale). A similar dynamic process has not been observed for the AuGe(2) compound 3 or for the AuSn(2) derivatives [Au{SnR(HMDS)(2)}{Sn(HMDS)(2)(THT)}] [R = Bu (5), HMDS (6)], which have been prepared by treating complex 4 with LiR. The structures of compounds 1 and 3-6 have been determined by X-ray diffraction.     

Bi‐ and Polynuclear Transition‐Metal Carbon Tellurides

The first examples of bi‐ and polynuclear tellurocarbonyl complexes were obtained from the reactions of [W(≡CTe)(CO)₂(Tp*)]NEt₄ (Tp*=hydrotris(dimethylpyrazolyl)borate) with [MCl(PCy₃)]/TlPF₆ (M=Cu, Au) or [Au₂Cl₂(μ‐dppm)], which afford [WM(μ‐CTe)(PCy₃)(CO)₂(Tp*)] (M=Cu, Au) and [WAu₂(μ‐CTe)(μ‐dppm)(CO)₂(Tp*)]₃(PF₆)₃. In all cases it is specifically the tellurocarbonyl that assumes a bridging, but in each case distinct, role including examples of isotellurocarbonyl, semi‐bridging and σ–π coordination and combinations thereof. Tetrametallic complexes bridged by C₂Te and C₂Te₂ ligands are also described.     

Ruthenium bidentate phosphine complexes for the coordination and catalytic dehydrogenation of amine- and phosphine-boranes

Addition of the amine–boranes H₃B ? NH₂tBu, H₃B ? NHMe₂ and H₃B ? NH₃ to the cationic ruthenium fragment [Ru(xantphos)(PPh₃)(OH₂)H][BAr^F₄] ( 2 ; xantphos=4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene; BAr^F₄=[B{3,5‐(CF₃)₂C₆H₃}₄]^?) affords the η¹‐B? H bound amine–borane complexes [Ru(xantphos)(PPh₃)(H₃B ? NH₂tBu)H][BAr^F₄] ( 5 ), [Ru(xantphos)(PPh₃)(H₃B ? NHMe₂)H][BAr^F₄] ( 6 ) and [Ru(xantphos)(PPh₃)(H₃B ? NH₃)H][BAr^F₄] ( 7 ). The X‐ray crystal structures of 5 and 7 have been determined with [BAr^F₄] and [BPh₄] anions, respectively. Treatment of 2 with H₃B ? PHPh₂ resulted in quite different behaviour, with cleavage of the B? P interaction taking place to generate the structurally characterised bis‐secondary phosphine complex [Ru(xantphos)(PHPh₂)₂H][BPh₄] ( 9 ). The xantphos complexes 2 , 5 and 9 proved to be poor precursors for the catalytic dehydrogenation of H₃B ? NHMe₂. While the dppf species (dppf=1,1′‐bis(diphenylphosphino)ferrocene) [Ru(dppf)(PPh₃)HCl] ( 3 ) and [Ru(dppf)(η⁶‐C₆H₅PPh₂)H][BAr^F₄] ( 4 ) showed better, but still moderate activity, the agostic‐stabilised N‐heterocyclic carbene derivative [Ru(dppf)(ICy)HCl] ( 12 ; ICy=1,3‐dicyclohexylimidazol‐2‐ylidene) proved to be the most efficient catalyst with a turnover number of 76 h^?1 at room temperature.     

A Two‐Coordinate Cobalt(II) Imido Complex with NHC Ligation: Synthesis,Structure, and Reactivity

The synthesis, structural characterization, and reactivity of the first two‐coordinate cobalt complex featuring a metal–element multiple bond [(IPr)Co(NDmp)] ( 4 ; IPr=1,3‐bis(2′,6′‐diisopropylphenyl)imidazole‐2‐ylidene; Dmp=2,6‐dimesitylphenyl) is reported. Complex 4 was prepared from the reaction of [(IPr)Co(η²‐vtms)₂] (vtms=vinyltrimethylsilane) with DmpN₃. An X‐ray diffraction study revealed its linear C? Co? N core and a short Co? N distance (1.691(6) Å). Spectroscopic characterization and calculation studies indicated the high‐spin nature of 4 and the multiple‐bond character of the Co? N bond. Complex 4 effected group‐transfer reactions to CO and ethylene to form isocyanide and imine, respectively. It also facilitated E? H (E=C, Si) σ‐bond activation of terminal alkyne and hydrosilanes to produce the corresponding cobalt(II) alkynyl and cobalt(II) hydride complexes as 1,2‐addition products.     

The Coordination Behavior of Oxygen-depleted Calixarenes towards d10 Noble Metal Ions

A calix[4]arene, in which two of the phenol functions are replaced by pyrazole units, [H₂(bpzCal)], was investigated as a ligand for Cu⁺, Ag⁺ and Au⁺ ions. Using [Cu(MeCN)₄]BF₄ and AgSbF₆ as the precursors, complexes [MH₂(bpzCal)]X (M = Cu, X = BF_4; M = Ag, X = SbF₆) were formed, where the calixarene ligands adopt a 1,3-alternate structure and the metal ions are coordinated linearly by the two pyrazolyl donors. [CuH₂(bpzCal)]BF₄ displayed a – for copper(I) complexes – unusual stability towards O₂, which is due to the steric protection of the Cu^I center. By contrast a dinuclear copper(I) complex [Cu₂(bpzCal)] that was obtained through treatment of [H₂(bpzCal)] with two equivalents of Cu(HMDS) is rather sensitive towards O₂. The preparation of a gold complex required the employment of a gold precursor, which contains one labile and one stabilizing neutral ligand, namely [(PPh₃)Au(NCMe)]SbF₆, which led to the formation of [(PPh₃)AuH₂(bpzCal)]SbF₆. In this complex [H₂(bpzCal)] acts only as a monodentate ligand for the gold center. Taken together, the results demonstrate the potential of [H₂(bpzCal)] in providing rather different coordination spheres for metal ions.     

Synthesis,Characterization, and Reactivity of Cationic Gold Diarylallenylidene Complexes

Methoxide abstraction from gold acetylide complexes of the form (L)Au[η¹‐C≡CC(OMe)ArAr′] (L=IPr, P(^tBu)₂(ortho‐biphenyl); Ar/Ar′=C₆H₄X where X=H, Cl, Me, OMe) with trimethylsilyl trifluoromethanesulfonate (TMSOTf) at ?78 °C resulted in the formation of the corresponding cationic gold diarylallenylidene complexes [(L)Au=C=C=CArAr′]⁺ OTf^? in ≥85±5 % yield according to ¹H NMR analysis. ¹³C NMR and IR spectroscopic analysis of these complexes established the arene‐dependent delocalization of positive charge on both the C1 and C3 allenylidene carbon atoms. The diphenylallenylidene complex [(IPr)Au=C=C=CPh₂]⁺ OTf^? reacted with heteroatom nucleophiles at the allenylidene C1 and/or C3 carbon atom.     

Terminal and Bridging Parent Amido 1,5‐Cyclooctadiene Complexes of Rhodium and Iridium

The ready availability of rare parent amido d⁸ complexes of the type [{M(μ‐NH₂)(cod)}₂] (M=Rh ( 1 ), Ir ( 2 ); cod=1,5‐cyclooctadiene) through the direct use of gaseous ammonia has allowed the study of their reactivity. Both complexes 1 and 2 exchanged the di‐olefines by carbon monoxide to give the dinuclear tetracarbonyl derivatives [{M(μ‐NH₂)(CO)₂}₂] (M=Rh or Ir). The diiridium(I) complex 2 reacted with chloroalkanes such as CH₂Cl₂ or CHCl₃, giving the diiridium(II) products [(Cl)(cod)Ir(μ‐NH₂)₂Ir(cod)(R)] (R=CH₂Cl or CHCl₂) as a result of a two‐center oxidative addition and concomitant metal–metal bond formation. However, reaction with ClCH₂CH₂Cl afforded the symmetrical adduct [{Ir(μ‐NH₂)(Cl)(cod)}₂] upon release of ethylene. We found that the rhodium complex 1 exchanged the di‐olefines stepwise upon addition of selected phosphanes (PPh₃, PMePh₂, PMe₂Ph) without splitting of the amido bridges, allowing the detection of mixed COD/phosphane dinuclear complexes [(cod)Rh(μ‐NH₂)₂Rh(PR₃)₂], and finally the isolation of the respective tetraphosphanes [{Rh(μ‐NH₂)(PR₃)₂}₂]. On the other hand, the iridium complex 2 reacted with PMe₂Ph by splitting the amido bridges and leading to the very rare terminal amido complex [Ir(cod)(NH₂)(PMePh₂)₂]. This compound was found to be very reactive towards traces of water, giving the more stable terminal hydroxo complex [Ir(cod)(OH)(PMePh₂)₂]. The heterocyclic carbene IPr (IPr=1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene) also split the amido bridges in complexes 1 and 2 , allowing in the case of iridium to characterize in situ the terminal amido complex [Ir(cod)(IPr)(NH₂)]. However, when rhodium was involved, the known hydroxo complex [Rh(cod)(IPr)(OH)] was isolated as final product. On the other hand, we tested complexes 1 and 2 as catalysts in the transfer hydrogenation of acetophenone with iPrOH without the use of any base or in the presence of Cs₂CO₃, finding that the iridium complex 2 is more active than the rhodium analogue 1 .     

Synthesis and Catalytic Use of Gold(I) Complexes Containing a Hemilabile Phosphanylferrocene Nitrile Donor

Removal of the chloride ligand from [AuCl( 1 ‐κP)] ( 2 ) containing a P‐monodentate 1′‐(diphenylphosphanyl)‐1‐cyanoferrocene ligand ( 1 ), by using silver(I) salts affords cationic complexes of the type [Au( 1 )]X, which exist either as cyclic dimers [Au( 1 )]₂X₂ ( 3 a , X=SbF₆; 3 c , X=NTf₂) or linear coordination polymers [Au( 1 )]_nX_n ( 3 a′ , X=SbF₆; 3 b′ , X=ClO₄), depending on anion X and the isolation procedure. As demonstrated for 3 a′ , the polymers can be readily cleaved by the addition of donors, such as Cl^?, tetrahydrothiophene (tht) or 1 , giving rise to the parent compound 2 , [Au(tht)( 1 ‐κP)][SbF₆] ( 5 a ) or [Au( 1 ‐κP)₂][SbF₆] ( 4 a ), respectively, of which the last two compounds can also be prepared by stepwise replacement of tht in [Au( 1 ‐κP)₂][SbF₆]. The particular combination of a firmly coordinated (phosphane) and a dissociable (nitrile) donor moieties renders complexes 3/3′ attractive for catalysis because they can serve as shelf‐stable precursors of coordinatively unsaturated Au^I fragments, analogous to those that result from the widely used [Au(PR₃)(RCN)]X catalysts. The catalytic properties of the Au‐ 1 complexes were evaluated in model annulation reactions, such as the synthesis of 2,3‐dimethylfuran from (Z)‐3‐methylpent‐2‐en‐4‐yn‐1‐ol and oxidative cyclisation of alkynes with nitriles to produce 2,5‐disubstituted 1,3‐oxazoles. Of the compounds tested ( 2 , 3 a′ , 3 b′ , 3 a , 4 a and 5 a ), the best results were consistently achieved with dimer 3 c , which has good solubility in organic solvents and only one firmly bound donor at the gold atom. This compound was advantageously used in the key steps of annuloline and rosefuran syntheses.     

N-Heterocyclic Carbene Analogues of Nucleophilic Phosphinidene Transition Metal Complexes

Chloride abstraction from the complexes [(η⁶-p-cymene){(IDipp)P}MCl] ( 2 a , M=Ru; 2 b , M=Os) and [(η⁵-C₅Me₅){(IDipp)P}IrCl] ( 3 b , IDipp=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) with sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaBAr^F) in the presence of trimethylphosphine (PMe₃), 1,3,4,5-tetramethylimidazolin-2-ylidene (^MeIMe) or carbon monoxide (CO) afforded the complexes [(η⁶-p-cymene){(IDipp)P}M(PMe₃)]BAr^F] ( 4 a , M=Ru; 4 b , M=Os), [(η⁶-p-cymene){(IDipp)P}Os(^MeIMe)]BAr^F] ( 5 ) and [(η⁵-C₅Me₅){(IDipp)P}IrL][BAr^F] ( 6 , L=PMe₃; 7 , L=^MeIMe; 8 , L=CO). These cationic N-heterocyclic carbene-phosphinidene complexes feature very similar structural and spectroscopic properties as prototypic nucleophilic arylphosphinidene complexes such as low-field ³¹P NMR resonances and short metal-phosphorus double bonds. Density functional theory (DFT) calculations reveal that the metal-phosphorus bond can be described in terms of an interaction between a triplet [(IDipp)P]⁺ cation and a triplet metal complex fragment ligand with highly covalent σ- and π-contributions. Crystals of the C−H activated complex 9 were isolated from solutions containing the PMe₃ complex, and its formation can be rationalized by PMe₃ dissociation and formation of a putative 16-electron intermediate [(η⁵-C₅Me₅)Ir{P(IDipp)}I][BAr^F], which undergoes C−H activation at one of the Dipp isopropyl groups and addition along the iridium-phosphorus bond to afford an unusual η³-benzyl coordination mode.