Rhodium-catalyzed nondecarbonylative addition reaction of ClCOCOOC2H5 to alkynes

Addition of ethoxalyl chloride (ClCOCOOEt) to terminal alkynes at 60 degrees C in the presence of a rhodium(I)-phosphine complex catalyst chosen from a wide range affords 4-chloro-2-oxo-3-alkenoates regio- and stereoselectively. Functional groups such as chloro, cyano, alkoxy, siloxy, and hydroxy are tolerated. The oxidative addition of ethoxalyl chloride to [RhCl(CO)(PR(3))(2)] proceeds readily at 60 degrees C or room temperature and gives [RhCl(2)(COCOOEt)(CO)(PR(3))(2)] (PR(3) = PPh(2)Me, PPhMe(2), PMe(3)) complexes in high yields. The structure of [RhCl(2)(COCOOEt)(CO)(PPh(2)Me)(2)] was confirmed by X-ray crystallography. Thermolysis of these ethoxalyl complexes has revealed that those ligated by more electron-donating phosphines are fairly stable against decarbonylation and reductive elimination. [RhCl(2)(COCOOEt)(CO)(PPh(2)Me)(2)] reacts with 1-octyne at 60 degrees C to form ethyl 4-chloro-2-oxo-3-decenoate. The catalysis is therefore proposed to proceed by oxidative addition of ethoxalyl chloride, insertion of an alkyne into the Cl--Rh bond of the resulting intermediate, and reductive elimination of alkenyl-COCOOEt.     

A mechanistic investigation into the elimination of phosphonium salts from rhodium-TRIPHOS complexes under methanol carbonylation conditions

Phosphine modified rhodium complexes are currently the topic of considerable research as methanol carbonylation catalysts, but often suffer from poor stability. This paper reports on an investigation into how coordination mode affects the elimination of phosphonium salts from rhodium complexes, namely [trans-RhCl(CO)(PPh(3))(2)] , [RhCl(CO)(dppe)] , [RhCl(CO)(dppb)](2), [Rh(TRIPHOS)(CO)(2)]Cl . These complexes are all potential pre-catalysts for methanol carbonylation. The reaction of these complexes with methyl iodide at 140 degrees C under both N(2) and CO atmospheres has been studied and has revealed clear differences in the stability of the corresponding Rh(iii) complexes. In contrast to both monomeric and dimeric that react cleanly with CH(3)I to give stable Rh(iii) acetyl complexes, forms a novel bidentate complex after the elimination of the one arm of the ligand as a quaternised phosphonium salt. The structure of this complex has been determined spectroscopically and using X-ray crystallography. The mechanism of formation of this novel complex has been investigated using (13)CH(3)I and strong evidence that supports a dissociative mechanism as the means of phosphine loss from the rhodium centre is provided.     

Sterically hindered electron-withdrawing ligands: the reactions of N-carbazolyl phosphines with rhodium and palladium centres

The series of N-carbazolyl phosphines PPh(3-n)(NC(12)H(8))(n)(n= 1, L1; n= 2, L2; n= 3, L3) has been synthesised using BuLi to generate the N-carbazolyl lithium salt, followed by reaction with the appropriate chlorophosphine. The reactions between [Rh(mu-Cl)(CO)(2)](2) and four equivalents of L1 or L2 gave [RhCl(CO)(L1)(2)] 1 and [RhCl(CO)(L2)(2)] 2, though attempts to synthesise the analogous complex using L3 resulted in the formation of [Rh(mu-Cl)(CO)(L3)](2) 3 instead. The inability of L3 to cleave the chloride bridges can be related to its considerable steric requirements. The electronic properties of L1-3 were assessed by comparison of the nu(CO) values of the [Rh(acac)(CO)(L1-3)] complexes 4-6. The increase in number of N-carbazolyl substituents at the phosphorus atom results in a decrease of the sigma-donor and increase in the pi-acceptor character in the order L1 < L2 < L3. In the reactions of L1-3 with [PdCl(2)(cod)] only L1 was able to displace cod from the metal centre and form [PdCl(2)(L1)(2)] 7. The use of [PdCl(2)(NCMe)(2)] instead of [PdCl(2)(cod)] resulted in the formation of the complexes [PdCl(2)(L1)(2)] 7 from L1, the cyclometallated complex [Pd(mu-Cl)[P(NC(12)H(8))(2)(NC(12)H(7))-kappa(2)P,C]](2) 8 from L3 , and a mixture of [PdCl(2)(L2)(2)] 9 and [Pd(mu-Cl)[PPh(NC(12)H(8))(NC(12)H(7))-kappa(2)P,C]](2) 10 from L2 . The reaction of L3 with [Pd(OAc)(2)] produced the cyclometallated complex [Pd(mu-O(2)CCH(3))[P(NC(12)H(8))(2)(NC(12)H(7))-kappa(2)P,C]](2) 11. The reaction of L3 with [Pd(2)(dba)(3)].CHCl(3) produced the 14-electron complex [Pd(L3)(2)] 12. The X-ray crystal structures of six complexes are reported, all of which show the presence of C-H...Pd hydrogen bonding.     

Rh(I) coordination chemistry of chiral alpha-aminophosphine(eta6-arene)chromium tricarbonyl ligands

The diastereoselective addition of Ph(2)PH to the chiral ortho-substituted eta(6)-benzaldimine complexes (eta(6)-o-X-C(6)H(4)CH=NAr)Cr(CO)(3) (1, X = MeO, Ar = p-C(6)H(4)OMe; 2, X = Cl, Ar = Ph) leads to the formation of the corresponding chiral aminophosphines (alpha-P,N) Ph(2)P-CH(Ar(1))-NHAr(2) (3, Ar(1) = o-C(6)H(4)(OCH(3))[Cr(CO)(3)], Ar(2) = p-C(6)H(4)OCH(3); 4, Ar(1) = o-C(6)H(4)Cl[Cr(CO)(3)], Ar(2) = Ph) in equilibrium with the starting materials. The uncomplexed benzaldimine (o-ClC(6)H(4)CH=NPh), 2', analogously produces an equilibrium amount of the corresponding aminophosphine Ph(2)P-CH(Ar(1))-NHAr(2) (4', Ar(1) = o-C(6)H(4)Cl, Ar(2) = Ph). Depending on the equilibrium constant, the subsequent addition of (1)/(2) equiv of [RhCl(COD)](2) (COD = 1,5-cyclooctadiene) leads to either Ph(2)PH oxidative addition in the case of 3 or to the corresponding [RhCl(COD)(alpha-P,N)] complexes [RhCl(COD)(Ph(2)P-CH[o-C(6)H(4)Cl[Cr(CO)(3)]]-NHPh)] (5) and [RhCl(COD)(Ph(2)P-CH(o-C(6)H(4)Cl)-NHPh)] (5') in the cases of the aminophosphines 4 and 4'. The addition of the latter ligands, as racemic mixtures, to (1)/(4) equiv of [Rh(CO)(2)Cl](2) leads to the [RhCl(CO)(alpha-P,N)(2)] complexes [RhCO(Ph(2)P-CH[o-C(6)H(4)Cl[Cr(CO)(3)]]-NHPh)(2)Cl] (7) or [RhCO(Ph(2)P-CH(o-C(6)H(4)Cl)-NHPh)(2)Cl] (7') as mixtures of (R(C),S(C))/(S(C),R(C)) and (R(C),R(C))/(S(C),S(C)) diastereomers. The rhodium complexes 5 and 7' have been fully characterized by IR and (31)P NMR spectroscopies and X-ray crystallography. These compounds exhibit intramolecular Rh-Cl.H-N interactions in the solid state and in solution. The stability of the new rhodium complexes has been studied under different CO pressures. Under 1 atm of CO, 5 is converted to an unstable complex [RhCl(CO)(2)(alpha-P,N)], 6, which undergoes ligand redistribution leading to 7 plus an unidentified complex. This reaction is inhibited under higher CO or syngas pressure, as confirmed by the observation of the same catalytic activity in hydroformylation when styrene was added to a catalytic mixture that was either freshly prepared or left standing for 20 h under high CO pressure.     

Complexes dinucleaires pontes des metaux d8: VII. Reactions d'addition oxydante d'halogenures d'alkyle et d'acycle aux complexes μ-halogenes du rhodium(i) [RhX(CO)(PR3)]2. Structure cristalline de [RhCl(CO)(PMe2Ph)(Me)(Br)]2

The halogen bridged binuclear complexes of rhodium(I) [RhCl(CO)(PR₃)]₂ undergo oxidative addition with methyl halides to yield the complexes [RhCl(CO)(PR₃)(Me)(X)]₂ (X = Cl, Br). The crystal and molecular structures of [RhCl(CO)(PMe₂Ph)(Me)(Br)]₂ have been determined from a single crystal by use of X-ray crystallographic methods. The space group is Pca2₁ or Pacm with a 19.501(5), b 10.381(4), c 13.641(5) e? Z = 4. Parameters of 30 nonhydrogen atoms in the space group Pca2₁ were refined by the full-matrix least squares technique to a conventional R factor of 0.073. In a binuclear unit, each rhodium atom is in an octahedral environment being bonded to a carbonyl group, a methyl group and a tertiary phosphine ligand and three halogen atoms for which, due to a disorder phenomenon, the diffusion factors have been determined as the average between those of chlorine and bromine atoms. In solution the cis-migration of the methyl groups occurs, leading to the acetyl complexes. In the case of CH₃I, it is shown that an equilibrium is present in solution: [RhCl(CO)(PR₃(Me)(I)]₂ ? [RhCl(COMe)(PR₃)(I)(solvant)]₂] Carbonylation reactions shift this equilibrium to give the complexes [RhCl(CO)(COMe)(PR₃(I)]₂. Such complexes are readily prepared by direct oxidative addition of acyl halides to the compounds [RhCl(CO)(PR₃)]₂.     

Synthesis of [Ag(NH=CMe(2))(2)]ClO(4) and its use as a source of acetimine. 1. Synthesis of the first acetimine rhodium complexes and the first crystal structure of a diacetonamine complex

The reaction of AgClO(4) and NH(3) in acetone gave [Ag(NH=CMe(2))(2)]ClO(4) (1). The reactions of 1 with [RhCl(diolefin)](2) or [RhCl(CO)(2)](2) (2:1) gave the bis(acetimine) complexes [Rh(diolefin)(NH=CMe(2))(2)]ClO(4) [diolefin = 1,5 cyclooctadiene = cod (2), norbornadiene = nbd (3)] or [Rh(CO)(2)(NH=CMe(2))(2)]ClO(4) (4), respectively. Mono(acetimine) complexes [Rh(diolefin)(NH=CMe(2))(PPh(3))]ClO(4) [diolefin = cod (5), nbd (6)] or [RhCl(diolefin)(NH=CMe(2))] [diolefin = cod (7), nbd (8)] were obtained by reacting 2 or 3 with PPh(3) (1:1) or with Me(4)NCl (1:1.1), respectively. The reaction of 4 with PR(3) (R = Ph, To, molar ratio 1:2) led to [Rh(CO)(NH=CMe(2))(PR(3))(2)]ClO(4) [R = Ph (9), C(6)H(4)Me-4 = To (10)] while cis-[Rh(CO)(NH=CMe(2))(2)(PPh(3))]ClO(4) (11) was isolated from the reaction of 1 with [RhCl(CO)(PPh(3))](2) (1:1). The crystal structures of 5 and [Ag[H(2)NC(Me)(2)CH(2)C(O)Me](PTo(3))]ClO(4) (A), a product obtained in a reaction between NH(3), AgClO(4), and PTo(3), have been determined.     

On the Existence of a Pyramidality Effect in d(8).d(8) Contacts. Theoretical Study and Structural Correlation

A qualitative molecular orbital study of d(8).d(8) contacts, using as models the dimers of [RhCl(CO)(3)] and cis-[PtCl(2)(CO)(2)], is presented, focusing on the effect of the pyramidalization of the metal atom on the strength of the metal-metal interaction. The existence of a pyramidality effect in dimers of d(8)-ML(4) complexes is supported also by the results of ab initio MP2 calculations on the dimer of cis-[PtCl(2)(CO)(2)]. A structural database analysis shows that a correlation between the pyramidality and the M.M distance exists for several families of dimers, oligomers, and polymers of square planar complexes of Ni(II), Pd(II), Pt(II), and Au(III). The importance of the pyramidality effect in those compounds is discussed in comparison with similar effects in binuclear complexes with metal-metal bonds of different multiplicities.     

An unprecedented dinuclear alkylrhodium(III) complex built up by two 14-electron [RhCl2(alkyl)(PR3)] units

Reaction of HCl with [RhCl(C2H4)(PR3)]2 affords the dinuclear alkylrhodium(III) complex [RhCl2(C2H5)(PR3)]2, the structure of which has been determined crystallographically. PR3 is the formerly unknown trialkyl phosphine tBu2PCH2CH2C6H3-2,6-Me2, prepared in three steps from tBuPCl2. Treatment of the title compound with CO gives the mononuclear rhodium dicarbonyl cis-[RhCl(CO)2(PR3)], being the first fully characterized complex of this type.     

The bridging function of an apparently nonbridging ligand: dinuclear rhodium complexes with Rh(mu-SbR3)Rh as a molecular unit

Novel dinuclear rhodium complexes of the general composition [Rh2Cl2(mu-CRR')2(mu-SbiPr3)] (4-6) were prepared by thermolysis of the mononuclear precursors trans-[RhCl(=CRR')(SbiPr3)2] in excellent yield. The X-ray crystal structure analysis of 4 (R = R' = Ph) confirms the symmetrical bridging position of the stibane ligand. Related compounds [Rh2Cl2(mu-CPh2)(mu-CRR')(mu-SbiPr3)] (7, 8) with two different carbene units were obtained either from trans-[RhCl(=CPh2)(SbiPr3)2] (1) and RR'CN2 or by a conproportionation of 4 and 5 (R = R' = p-Tol) or 4 and 6 (R= Ph, R' = p-Tol), respectively. While CO reacts with 4 to give the polymeric product [[RhCl(CPh2)(CO)]n] (9), tert-butyl isocyanide replaces the bridging stibane and yields [Rh2Cl2(mu-CPh2)2(mu-CNtBu)] (10). The reaction of 4 with tertiary phosphanes PR3 leads to complete bridge cleavage and affords the mononuclear compounds trans-[RhCl(=CPh2)(PR3)2] (11-15). In contrast, treatment of 4 with SbMe3 and SbEt3 yields the related triply bridged complexes [Rh2Cl2(mu-CPh2)2(mu-SbR3)] (16, 17) by substitution of SbiPr3 for the smaller stibanes. The displacement of the chloro ligands in 4-6 and 10 by n5-cyclopentadienyl gives the dinuclear complexes [(n5-C5H5)2Rh2(mu-CRR')2] (18-20) and [(n5-C5H5)2Rh2(mu-CPh2)2(mu-CNtBu)] (21), of which 18 (R = R' = Ph) was characterized crystallographically.     

Hydrogenation studies involving halobis(phosphine)-rhodium(I) dimers: use of parahydrogen induced polarisation to detect species present at low concentration

Reaction of [RhCl(PPh3)2]2 with parahydrogen revealed that the binuclear dihydride [Rh(H)2(PPh3)2mu-Cl)2Rh(PPh3)2] and the tetrahydride complex [Rh(H)2(PPh3)2(mu-Cl)]2 are readily formed. While magnetisation transfer from free H2 into both the hydride resonances of the tetrahydride and [Rh(H)2Cl(PPh3)3] is observable, neither transfer into [Rh(H)2(PPh3)2(mu-Cl)2Rh(PPh3)2] nor transfer between the two binuclear complexes is seen. Consequently [Rh(H)2(PPh3)2(mu-Cl)]2 and [Rh(H)2(PPh3)2(mu-Cl)2Rh(PPh3)2] are not connected on the NMR timescale by simple elimination or addition of H2. The rapid exchange of free H2 into the tetrahydride proceeds via reversible halide bridge rupture and the formation of [Rh(H)2(PPh3)2(mu-Cl)RhCl(H)2(PPh3)2]. When these reactions are examined in CD2Cl2, the formation of the solvent complex [Rh(H)2(PPh3)2(mu-Cl)2Rh(CD2Cl2)(PPh3)] and the deactivation products [Rh(Cl)(H)PPh3)2(mu-Cl)(mu-H)Rh(Cl)(H)PPh3)2] and [Rh(Cl)(H)(CD2Cl2)(PPh3)(mu-Cl)(mu-H)Rh(Cl)(H)PPh3)2] is indicated. In the presence of an alkene and parahydrogen, signals corresponding to binuclear complexes of the type [Rh(H)2(PPh3)2(mu-Cl)(2)(Rh)(PPh3)(alkene)] are detected. These complexes undergo intramolecular hydride interchange in a process that is independent of the concentration of styrene and catalyst and involves halide bridge rupture, followed by rotation about the remaining Rh-Cl bridge, and bridge re-establishment. This process is facilitated by electron rich alkenes. Magnetisation transfer from the hydride ligands of these complexes into the alkyl group of the hydrogenation product is also observed. Hydrogenation is proposed to proceed via binuclear complex fragmentation and trapping of the resultant intermediate [RhCl(H)2PPh3)2] by the alkene. Studies on a number of other binuclear dihydride complexes including [(H)(Cl)Rh(PMe3)2(mu-H)(mu-Cl)Rh(CO)(PMe3)], [(H)2Rh(PMe3)2(mu-Cl)2Rh(CO)(PMe3)] and [HRh(PMe3)2(mu-H)(mu-Cl)2Rh(CO)(PMe3)] reveal that such species are able to play a similar role in hydrogenation catalysis. When the analogous iodide complexes [RhIPPh3)2]2 and [RhI(PPh3)3] are examined, [Rh(H)2(PPh3)2(mu-I)2Rh(PPh3)2], [Rh(H)2(PPh3)2(mu-I)]2 and [Rh(H)2I(PPh3)3] are observed in addition to the corresponding binuclear alkene-dihydride products. The higher initial activity of these precursors is offset by the formation of the trirhodium phosphide bridged deactivation product, [[(H)(PPh3)Rh(mu-H)(mu-I)(mu-PPh2)Rh(H)(PPh3)](mu-I)2Rh(H)2PPh3)2]     

Selective cleavage of P-N bonds and the conversion of rhodium N-pyrrolyl phosphine complexes into diphosphoxane-bridged dimers

Rhodium(I) complexes trans-[RhCl(CO)(PR(2)[NC(4)H(3)C(O)Me-2])(2)] (R = Ph, NC(4)H(4)) react with water to give the diphosphoxane-bridged dimers [Rh(2)Cl(2)(CO)(2)(mu-PR(2)OPR(2))(2)] following cleavage of the P-N bonds to the 2-acetyl-N-pyrrolyl groups. The two dimers have been crystallographically characterized and show a number of structural differences, with the PPh(2)OPPh(2) compound possessing semibridging chloride and carbonyl ligands whereas the P(NC(4)H(4))(2)OP(NC(4)H(4))(2) compound contains only terminal chlorides and carbonyls. No evidence for cleavage of the P-N bonds involving the unfunctionalized N-pyrrolyl groups in trans-[RhCl(CO)(P[NC(4)H(4)](2)[NC(4)H(3)C(O)Me-2])(2)] was observed.     

Substitution reactions with [ReBr(2)(CO)(2)(NCCH(3))(2)](-): a convenient route to complexes with the cis-[Re(CO)(2)](+) core

Water- and air-stable complexes comprising the cis-[Re(CO)(2)](+) core can be synthesized from the (Et(4)N)[ReBr(2)(NCCH(3))(2)(CO)(2)] precursor . Complex showed distinctly different chemical and electronic behaviour compared to [ReBr(3)(CO)(3)](2-). Substituting the two bromides in with imidazole-like ligands or alpha,alpha'-diimines gave new complexes with potential applications in bioinorganic chemistry and photochemistry. The two acetonitrile ligands are very stably bound and could not be replaced. Under CO pressure, the uncommon complex mer-[ReBr(NCCH(3))(2)(CO)(3)] was formed from . The reaction of with the tetradentate ligand bis(2-pyridylmethyl)glycine (BPG) finally induced a four fold substitution at the metal center to form a [Re(CO)(2)(L(4))](+)-type complex.     

Transition metal complexes bearing a 2,2-bis(3,5-dimethylpyrazol-1-yl)propionate ligand: one methyl more matters

The new N,N,O ligand 2,2-bis(3,5-dimethylpyrazol-1-yl)propionic acid (2,2-Hbdmpzp) (2) and its transition metal complexes [Mn(2,2-bdmpzp)(CO)(3)] (3), [Re(2,2-bdmpzp)(CO)(3)] (4), [Cu(2,2-bdmpzp)(2)] (5), and [Ru(2,2-bdmpzp)Cl(L)(PPh(3))] [L = PPh(3) (6), N(2) (7), CO (8a/b), SO(2) (9a/b)] have been synthesized, characterized and compared to analogous complexes bearing a bis(3,5-dimethylpyrazol-1-yl)acetic acid. It was found that the additional methyl group has a remarkable influence on the stability and reactivity of transition metal complexes.     

A study of M-X-BR3 (M = Pt, Pd or Rh; X = Cl or I) interactions in square planar ambiphilic ligand complexes: structural, spectroscopic, electrochemical and computational comparisons with borane-free analogues

Reaction of [PtCl(2)(COD)] and [PtI(2)(COD)] with 2,7-di-tert-butyl-5-diphenylboryl-4-diphenylphosphino-9,9-dimethylthioxanthene (TXPB) afforded square planar [PtCl(2)(TXPB)] (1B) and [PtI(2)(TXPB)] (4B), both of which were crystallographically characterized. Single-crystal X-ray quality crystals were also obtained for [PdCl(2)(TXPB)] (2B; Emslie et al., Organometallics, 2008, 27, 5317) as 2B·2CH(2)Cl(2) and solvent-free 2B. Both the chloro and iodo TXPB complexes exhibit metal-halide-borane bridging interactions similar to those in previously reported [RhCl(CO)(TXPB)] (3B) and [RhI(CO)(TXPB)] (5B) (Emslie et al., Organometallics, 2006, 25, 583 and Inorg. Chem., 2010, 49, 4060). To facilitate a more detailed analysis of M-X-BR(3) (X = Cl and I) interactions, a borane-free analogue of the TXPB ligand, 2,7-di-tert-butyl-4-diphenylphosphino-9,9-dimethylthioxanthene (TXPH), was prepared. Reaction with [PtX(2)(COD)] (X = Cl or I), [PdCl(2)(COD)] and 0.5 [{RhCl(CO)(2)}(2)] provided square planar [PtCl(2)(TXPH)] (1H), [PdCl(2)(TXPH)] (2H), [RhCl(CO)(TXPH)] (3H) and [PtI(2)(TXPH)] (4H). M-Cl-BR(3) and M-I-BR(3) bonding in 1B-5B was then probed through the use of structural comparisons, IR and NMR spectroscopy, cyclic voltammetry, and DFT calculations (Slater-type orbitals, Mayer bond orders, Hirshfeld charges, fragment analysis, SCF deformation density isosurfaces, and energy decomposition analysis).     

TcI(CN)3(CO)3]2- and [ReI(CN)3(CO)3]2- :case studies for the binding properties of CN- and CO

The cyano carbonyl complexes [(99)Tc(CN)(3)(CO)(3)]2- and [Re(CN)(3)(CO)(3)]2- were synthesized and fully characterized. These complexes are additional members of the well-known d(6) transition metal complex series [M(CN)(3)(CO)(3)](n-). The analytical data obtained in this study thus offer a unique opportunity to study similarities and differences of cyanide and carbonyl binding in transition metal complexes.     

Complexes dinucleaires pontes des metaux d8: II.preparation de deux series de composes du rhodium(I) pentacoordonne

In the course of the study of the reactivity of the dinuclear complexes [RhCl(CO)(C₂H₂)]₂ and [RhSR(CO)₂]₂ towards nucleophiles, two series of dinuclear pentacoordinated rhodium(I) complexes, [RhCl(CO)(C₂H₄)(amine)]₂ and [RhSR(CO)₂PR₃]₂, have been isolated.     

Synthesis and X-ray structures of water-soluble tris(hydroxymethyl)phosphine complexes of rhodium(I)

The water-soluble Rh(I)-THP complexes: RhCl(1,5-cod)(THP) (), [Rh(1,5-cod)(THP)(2)]Cl (), RhCl(THP)(4) (), and trans-RhCl(CO)(THP)(2) () have been synthesized and characterized, where THP = P(CH(2)OH)(3); - are the first potentially useful entries into Rh(I)-THP chemistry, while and are the first structurally characterized Rh(I)-THP complexes.     

Rhodium(I) and Silver(I) Complexes of 4, 5‐Dicyano‐1, 3‐dimesityl‐ and 4, 5‐Dicyano‐1, 3‐dineopentylimidazol‐2‐ylidene

The new N‐heterocyclic carbene (NHC) precursors 4, ‐dicyano‐1, ‐dimesityl‐ ( 9 ) and 4, 5‐dicyano‐1, 3‐dineopentyl‐2‐(pentafluorophenyl)imidazoline ( 14 ) were synthesized. The structure of 9 could be determined by X‐ray crystallography. With the 2‐pentafluorophenyl‐substituted imidazolines 9 and 14 , the [AgCl(NHC)], [RhCl(COD)(NHC)], and [RhCl(CO)₂(NHC)] complexes [NHC = 4, 5‐dicyano‐1, 3‐dimesitylimidazol‐2‐ylidene ( 3 ) and 4, 5‐dicyano‐1, 3‐dineopentylimidazol‐2‐ylidene ( 4 )] were obtained. Crystal structures of [AgCl( 3 )] ( 15 ), [RhCl(COD)( 3 )] ( 17 ), [RhCl(COD)( 4 )] ( 18 ), and [RhCl(CO)₂( 3 )] ( 19 ) were solved and with the crystal data of 19 , the percent buried volume ( %V_bur) of 31.8(±0.1) % was determined for NHC 3 . Infrared spectra of the imidazolines 9 and 14 and of the complexes 15 – 20 were recorded and the CO stretching frequencies of complexes 19 and 20 were used to determine the Tolman electronic parameters of the newly obtained NHCs 3 (TEP: 2060 cm^–1) and 4 (TEP: 2061 cm^–1), thus proving that 1, 3‐substitution of maleonitrile‐NHCs does not have a significant effect for the high π‐acceptor strength of these carbenes.     

Reactivity of novel N,N'-diphosphino-silanediamine-based rhodium(I) derivatives

The coordination abilities of the novel N,N'-diphosphino-silanediamine ligand of formula SiMe(2)(NtolPPh(2))(2) (SiNP, 1) have been investigated toward rhodium, and the derivatives [RhCl(SiNP)](2) (2), [Rh(SiNP)(COD)][BF(4)] (3), and Rh(acac)(SiNP) (4) have been synthesized. The stability of the dinuclear frame of [RhCl(SiNP)](2) (2) toward incoming nucleophiles has been shown to be dependent on their π-acceptor ability. Indeed, the mononuclear complexes RhCl(SiNP)(L) (L = CO, 5; CN(t)Bu, 6) have been isolated purely and quantitatively upon reaction of 2 with CO and CN(t)Bu, respectively. Otherwise, PPh(3) and RhCl(SiNP) equilibrate with Rh(Cl)(SiNP)(PPh(3)) (7). Carbon electrophiles such as MeI and 3-chloro-1-proprene afforded the oxidation of rhodium(I) to rhodium(III) and the formation of RhCl(2)(η(3)-C(3)H(5))(SiNP) (8) and Rh(Me)(I)(SiNP)(acac) (10), respectively. The methyl derivative 10 is thermally stable and does not react either with CO or with CN(t)Bu even in excess. Otherwise, RhCl(2)(η(3)-C(3)H(5))(SiNP) (8) is thermally stable but reacts with CO, affording 3-chloro-1-proprene and RhCl(SiNP)(CO) (5). Finally, upon reaction of Rh(acac)(SiNP) (4) and 3-chloro-1-proprene, RhCl(acac)(η(1)-C(3)H(5))(SiNP) (9a) and [Rh(acac)(η(3)-C(3)H(5))(SiNP)]Cl (9b) could be detected at 233 K. At higher temperatures, 9a and 9b smoothly decompose, affording the dinuclear derivative [RhCl(SiNP)](2) (2) and the CC coupling product 3-allylpentane-2,4-dione.     

Dimethylsulfoxide as a ligand for RhI and IrI complexes--isolation, structure, and reactivity towards X-H bonds (X=H, OH, OCH3)

Novel neutral and cationic Rh(I) and Ir(I) complexes that contain only DMSO molecules as dative ligands with S-, O-, and bridging S,O-binding modes were isolated and characterized. The neutral derivatives [RhCl(DMSO)(3)] (1) and [IrCl(DMSO)(3)] (2) were synthesized from the dimeric precursors [M(2)Cl(2)(coe)(4)] (M=Rh, Ir; COE=cyclooctene). The dimeric Ir(I) compound [Ir(2)Cl(2)(DMSO)(4)] (3) was obtained from 2. The first example of a square-planar complex with a bidentate S,O-bridging DMSO ligand, [(coe)(DMSO)Rh(micro-Cl)(micro-DMSO)RhCl(DMSO)] (4), was obtained by treating [Rh(2)Cl(2)(coe)(4)] with three equivalents of DMSO. The mixed DMSO-olefin complex [IrCl(cod)(DMSO)] (5, COD=cyclooctadiene) was generated from [Ir(2)Cl(2)(cod)(2)]. Substitution reactions of these neutral systems afforded the complexes [RhCl(py)(DMSO)(2)] (6), [IrCl(py)(DMSO)(2)] (7), [IrCl(iPr(3)P)(DMSO)(2)] (8), [RhCl(dmbpy)(DMSO)] (9, dmbpy=4,4'-dimethyl-2,2'-bipyridine), and [IrCl(dmbpy)(DMSO)] (10). The cationic O-bound complex [Rh(cod)(DMSO)(2)]BF(4) (11) was synthesized from [Rh(cod)(2)]BF(4). Treatment of the cationic complexes [M(coe)(2)(O=CMe(2))(2)]PF(6) (M=Rh, Ir) with DMSO gave the mixed S- and O-bound DMSO complexes [M(DMSO)(2)(DMSO)(2)]PF(6) (Rh=12; Ir=in situ characterization). Substitution of the O-bound DMSO ligands with dmbpy or pyridine resulted in the isolation of [Rh(dmbpy)(DMSO)(2)]PF(6) (13) and [Ir(py)(2)(DMSO)(2)]PF(6) (14). Oxidative addition of hydrogen to [IrCl(DMSO)(3)] (2) gave the kinetic product fac-[Ir(H)(2)Cl(DMSO)(3)] (15) which was then easily converted to the more thermodynamically stable product mer-[Ir(H)(2)Cl(DMSO)(3)] (16). Oxidative addition of water to both neutral and cationic Ir(I) DMSO complexes gave the corresponding hydrido-hydroxo addition products syn-[(DMSO)(2)HIr(micro-OH)(2)(micro-Cl)IrH(DMSO)(2)][IrCl(2)(DMSO)(2)] (17) and anti-[(DMSO)(2)(DMSO)HIr(micro-OH)(2)IrH(DMSO)(2)(DMSO)][PF(6)](2) (18). The cationic [Ir(DMSO)(2)(DMSO)(2)]PF(6) complex (formed in situ from [Ir(coe)(2)(O=CMe(2))(2)]PF(6)) also reacts with methanol to give the hydrido-alkoxo complex syn-[(DMSO)(2)HIr(micro-OCH(3))(3)IrH(DMSO)(2)]PF(6) (19). Complexes 1, 2, 4, 5, 11, 12, 14, 17, 18, and 19 were characterized by crystallography.