Helgard G. Raubenheimer

Oxidative addition of mono and bis(carbene) complexes derived from imidazolyl and thiazolyl gold(I) compounds

Abstract A series of cationic imidazolinylidene and thiazolinylidene gold(III) complexes was synthesized by the oxidative addition of halogens to the corresponding bis (carbene) gold(I) compounds. Similar reactions with the thiazolyl-derived mono (carbene) gold(I) complex only give mono (carbene) halogold(I) compounds. Quantum mechanical calculations employing the GAUSSIAN92 series of programs at the DFT/HF (hybrid density functional theory) level were carried out for the model complexes [Au{ovbar|CNHCHCHNH} 2 Cl 2 ] + and [Au- CNHCHCHNH ) 2 ) and compared to the molecular structure of the imidazolinylidene gold(III) compound [Au{ CNMeCHCHN Me} 2 Cl 2 ][CF 3 SO 3 ] as well as an analogous gold(I) complex.

Synthesis and characterization of neutral and cationic diamino carbene complexes of gold(I)

Abstract Bis(1-methylimidazolyl)aurate compounds were prepared by reacting 1-methylimidazol-2-yllithium and 1-methylbenzimidazol-2-yllithium with [AuCl(THT)] (THT = tetrahydrothiophene). Protonation or alkylation of the aurates yielded bis(carbene) complexes of the type [Au{ CNR 1 CR 2 CR 3 N (Me)} 2 ] + (R1 = H or Me; R2 = H or R2R3 = C4H4). The reaction of 1-methylimidazol-2-yllithium with [AuCl(PPh3)] afforded the same bis(carbene) cation after protonation or alkylation. Mono(diamino)gold(I)carbene complexes resulted from the sequential reactions of 1-methylimidazol-2-yllithium with [Au(C6F5)(THT)] or AuCN and CF3SO3Me or CF3SO3H. Complicating side-reactions such as homoleptic rearrangement and protonation on carbon rather than nitrogen were observed.

Sulphur-containing metal complexes: III. Tetracarbonyl(carbene—thio) complexes of chromium(0) and tungsten(0)

Abstract Reaction of α-lithiated sulphides with (CO) 6 Cr and (CO) 6 W followed by alkylation with (Et 3 O)BF 4 give the new series of neutral carbene-thiometal chelates of general formulae cis -(CO) 4 MC(OEt)[C(OH)C(S R 1 )R 2 ] (I) and cis -(CO) 4 MC(OEt)[C(OEt)C(S R 1 )R 2 ] (II). This route probably involves carbonyl insertion into a metalcarbene bond. Complexes of type II can also be prepared by treatment of pentacarbonyl(thio)metal complexes, (CO) 5 MS(CH 2 R 2 )R 1 , with BuLi, and subsequent alkylation. It is suggested that the second method proceeds via the generation of an anion α to a coordinated sulphur atom followed by a double ( cis-cis ) carbonylation.

Sulphur-containing metal complexes

Abstract The sulphides SR1R2 (R1 = C2H5; R2 = C2H5, CH2Ph) react with the carbene complexes [(CO)5CrC(OC2H5)R] (R = Bu, Ph), to produce the neutral pentacarbonyl(thio)chromium(0) complexes [(CO)5CrSR1R2], which have been characterized by chemical analysis, IR, NMR and mass spectra. Confirmation of the structures of the new complexes comes from a single-crystal X-ray study of (CO)5CrS(C2H5)CH2Ph, the first such study of a pentacarbonyl(dialkylthio)metal complex.

Characterization of mono(carbene) and bis(carbene) complexes of gold(I) derived from lithiated pyridine

Abstract The carbene complexes [Au(¯CNHCH=¯CHCH=¯C>H)Cl] ( 2 ) and [Au(¯CN(R) ¯CH=¯CHCH=¯C>H) 2 ][X] (R = H, X = Cl ( 4 )) (R = Me, X = CF 3 SO 3 ( 5 ) are formed when the products of the reactions between [Au(THT)Cl] (THT = tetrahydrothiophene) and 2-lithiopyridine are acidified with HCl or alkylated with CF 3 SO 3 Me. Compound 4 crystallizes with two molecules of H 2 O. The complex is monomeric and interacts with the water molecules and the chloride ion through a complex network of hydrogen bonds.

Cyclic voltammetry of heterocyclic Au(I) and Au(III) carbene complexes

Abstract Imidazolinylidene and thiazolinylidene complexes of gold in acetonitrile have been investigated by cyclic voltammetry. No Au(II) intermediate was observed during the redox reactions and Au(III) compounds form only by oxidative addition of halogens.

Sulphur-containing metal complexes: X. Reactions of [Fe(CO)5] with ethylenetrithiocarbonate. Structure of [Fe3(Co)9{CS(CH2)2S}S] containing a μ-dithiocarbene ligand

Abstract Four different conversions were observed when a mixture of [Fe(CO)5] and ethylenetrithiocarbonate was irradiated with ultraviolet light in tetrahydrofuran: (i) the thione bond in the ligand was broken and the sulphur atom was incorporated into a cluster to produce [Fe3(CO)9(μ3-S)2], (I); (ii) cleavage of the two CS single bonds occurred and the S(CH2)2S moiety was used to stabilize the complex [Fe2(CO)6{μ-S(CH2)2S}], (II); (iii) the ligand exhibited significant charge redistribution during coordination, in the compound [Fe2(CO)6-{S CS(CH 2 ) 2 S }], (III) and finally, (iv) the thione bond was cleaved and both fragments were used by the metalcarbonyl to yield the major product, [Fe3(CO)9{μ3- CS(CH 2 ) 2 S }(μ3-S)], (IV). A single crystal X-ray study of IV revealed that a dithiocarbene ligand caps an open iron triangle by forming a methylene bridge between two iron atoms and links up with the third iron atom via a sulphur atom.

Formation and Reactions of Organosulfur and Organoselenium Organometallic Compounds

Publisher Summary This chapter discusses the reactions of organosulfur and organoselenium compounds mediated by transition metals. In organic synthetic reactions, the scope and applications of organosulfur and organoselenium chemistry have increased tremendously. Organosulfur complexes of low oxidation state metals are generally less stable than their phosphorus counterparts, but this relative instability lends the complexes their reactivity. Organosulfur ligands are the reactive centers of the complexes. Low-valent nickel species catalyze the reaction between Grignard reagents and aryl or alkenyl sulfide in the preparation of alkylarenes, biaryls, and alkenes. In contrast, ultra violet (UV) irradiation of dithiane or trithiane in the presence of [Fe(CO)5] leads to the scission of only one C–S bond and the formation of an asymmetric complex. The molybdenum dimer can be converted, by alkylation, to a cation, which can be transformed into an anion by two-electron chemical reduction. Although the thiolysis of alkoxycarbenes to form thiocarbenes is not a new reaction, the new method, in which a catalyst is used, minimizes the formation of unwanted side products and dramatically increases the yield.

Sulphur-containing metal complexes : II. The crystal and molecular structures ofcis-[1,3-dithian-2-ylidene (hydroxy) methyl (ethoxy)carbene-c, s]-tetracarbonylchromium(o) andfac-[1,3-dithian-2-ylidene (ethoxy)methyl(ethoxy)carbene-c,s]t-butyl isocyanide tricarbonylchromium(O).

Abstract The structures of the title compounds cis - (CO)4 (I) and fac - CNCMe3)(CO)3 (II) have been determined from three dimensional X-ray data and confirm that their formation can be rationalized in terms of pathwaysinvolving respectively carbonyl insertion and double carbonylation. Refinement of the structures converged to final R-indices of 5.8 and 4.0% for respectively 1473 and 2650 independent reflections. The crystals of I are monoclinic, space group C2/c, with Z = 8 in a unit cell of dimensions : a 20.19(2), b 7.22(1), c 22.10(2) A, β = 106.9(1)°. For II the crystal data are: triclinic, space group P 1 , cell constants a 12.329(9), b 9.605(6), c 9.637(6) A, α 105.6(1), β 95.0(1), γ 94.9(1)°, Z = 2. Although part of chelating ring systems, the car- bene carbon-donor atoms have similar bonding characteris- tics to carbon donors in simpler alkoxycarbene complexes, and have CrC bond lengths comparable to the chromium- isonitrile linkage.

Sulphur-containing metal complexes: XXIII. Synthesis of new complexes containing the Fe2(CO)6S2 butterfly unit. Crystal and molecular structure of [Fe2(CO)6{μ-S2P(C6H4OMe-p)Fe(CO)4}], determined from two different crystal modifications☆

Abstract Diiron nonacarbonyl, [Fe 2 (CO) 9 ], reacts with Lawessons reagent, ( p MeOC 6 H 4 ){ovtsqb|P(=S)SP(=S)(C 6 H 4 OMe- p )S}, in tetrahydrofuran to give a number of products including [Fe 2 (CO) 6 {μ-S 2 P(C 6 H 4 OMe- p )Fe(CO) 4 }] (III). Single crystal X-ray analyses of this compound, show a dithionophosphine unit, S-P(R)-S (R = C 6 H 4 OMe- p ), to bridge the iron-iron bond of Fe 2 (CO) 6 via the two sulphur atoms and to link a Fe(CO) 4 moiety through coordination of the phosphorus atom. Reaction of Me 2 P(=S)P(=S)Me 2 with [Fe(CO) 5 ] under irradiation with ultraviolet light, affords the anti form of [Fe 2 (CO) 6 {μ-SPMe 2 } 2 ] (V) as major product. Two separate crystal structure determinations on compound III were carried out as it crystallizes under similar condition in two different crystal modifications. Two packing modes are possible because the near-mirror symmetry of the molecule allows two equivalent orientations in the crystal.