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The first N-heterocyclic carbene 1 featuring a cyclic sulfonamide structural motif has been prepared from 1,2,4-benzothiadiazine-1,1-dioxide. Within the six-membered heterocycle the carbene C atom is bound to an amino and a sulfonamido group. The (COD)Rh and (CO)2Rh complexes of the new NHC have been prepared and fully characterised including X-ray diffraction studies. Spectroscopic and structural data indicate that 1 is a poor overall donor (TEP: 2063 cm−1) and it has donor/acceptor properties that are close to those of related cyclic carboxamide substituted carbenes.

(NHC)Rh(CO)2Cl complexes interconvert reversibly in the presence of DMSO to the corresponding (NHC)Rh(DMSO)(CO)Cl complexes. The exchange of coordinated for free DMSO was investigated by NMR spectroscopy. The X-ray structure of compound 6a revealed that the CO ligand trans to the NHC had been replaced by S-bound DMSO. In addition, the reactivity of (NHC)Rh(CO)2Cl complexes towards other types of ligands like amines, NHCs and phosphines was investigated.

Methylation of 3-amino-1,2,4-triazole and 1-methyl-3-nitro-1,2,4-triazole provides access to three NHC-precursors. For the nitro compound only a monomethylation to the triazolium salt 3(OTf) is observed. The aminotriazole could be subsequently converted to mono- and dicationic carbene precursors 1I and 2(OTf)2, respectively. The nitro group on NHC 3 leads to a decrease of donor strength and a slightly enhanced acceptor character as compared to a related NHC lacking the nitro group. The cationic NHC 2 is the poorest donor within the series and shows a TEP value of 2072 cm−1. The properties of this species are dominated by its cationic nature while the influence of the NMe2 group is surprisingly small. X-ray diffraction studies suggest a guanidinium-like character for the NMe2 substituted compounds.

The synthesis and reactivity of the new cationic N-heterocyclic carbene 6 comprising a Cp*Ru+ fragment attached to the aromatic backbone of 1,3-dimethylperimidin-2-ylidene is reported. Carbene 6 forms Rh and Ir complexes of the type [(cod)ClM(6)]+ and [(CO)2ClM(6)]+. The analogous complexes of the neutral perimidin-2-ylidene 9 were prepared for comparison purposes. TEP values for both NHCs were calculated from the IR spectra of the carbonyl complexes. The TEP of the cationic carbene 6 (2062 cm−1) is shifted to higher wavenumbers compared to the neutral derivative 9 (2057 cm−1) indicating that the former ligand is a poorer overall donor. In addition, DFT calculations revealed a reduced HOMO–LUMO gap for the cationic system suggesting an increased π-acceptor character. Crystal structures of the related complexes [IrCl(cod)NHC(L)] with L = 6 and 9 were determined by X-ray diffraction and show only marginal differences in the geometrical parameters.

Imidazolium and benzimidazolium salts featuring exocyclic N-acyl or N-sulfonyl groups were prepared and converted in situ to the corresponding N-heterocyclic carbenes by deprotonation. The NHCs were further converted to group six adducts (sulfur and selenium) and metal complexes with Rh(I), Ir(I), Cu(I), Ni(II) and Fe(II). The N-acyl derivatives were found to be much more sensitive towards hydrolytic degradation than the N-sulfonyl compounds. IR spectroscopic analysis of NHC-carbonyl complexes revealed the N-acyl NHCs to be slightly better donors (TEP 2054–2055 cm−1) compared to the N-sulfonyl based ligands (TEP: 2056–2061 cm−1). Both classes are comparable to cyclic mono- and diamido carbenes regarding their donor properties.

Detailed studies concerning the reactivity of the dicationic organometallic carbene precursor 1 and its related free cationic carbene 2 have been carried out. While dication 1 is stable in O-donor solvents like acetone, nitromethane and even water, it is degraded by softer nucleophiles like acetonitrile or electron rich aromatics. In contrast to the hydrolytic stability of dication 1, the cationic carbene 2a reacts readily with water to form the ring-opened formamide derivative 5a. The mechanism of the hydrolytic cleavage reaction was analysed by DFT calculations.

The reaction of cyanuric chloride and two disubstituted derivatives with [Pd(PPh 3 ) 4 ] is described, leading to the trans -triazinyl complexes [(PPh 3 ) 2 Pd(C 3 N 3 R 2 )Cl] 2a–c (R = Ph ( a ), t -Bu ( b ), Cl ( c )) in good to excellent yield via oxidative addition. The complexes were fully characterized including X-ray structure determination.

Oxidative addition of N -alkyl-2-halopyrimidinium cations to [Pd(PPh 3 ) 4 ] gives straightforward access to the cationic complexes [(PPh 3 ) 2 (NHC)PdX]BF 4 ( 3a,b ) with pyrimidine-derived NHC-ligands. The new complexes were fully characterized including X-ray crystallography.

Reaction of 3,4-dimethylphospholylthallium (Tl- 1 ) with [Cp ∗ MCl 2 ] 2 (M = Rh, Ir) leads to the formation of the dimeric species [(Cp ∗ M) 2 (Me 2 C 4 H 2 P) 3 ] + 2 and 3 with bridging μ-η 1 :η 1 -phospholyl ligands. The phosphametallocenium sandwich complexes [Cp ∗ M(Me 2 C 4 (SiMe 3 ) 2 P)] + 7 (M = Rh) and 8 (M = Ir) could be obtained from the reaction of [Cp ∗ MCl 2 ] 2 and the 2,5-bis(trimethylsilyl)-1-trimethylstannylphosphole 6 , with the bulky trimethylsilyl groups preventing the phosphole from η 1 - and enforcing a η 5 -coordination. The structures of phospharhodocenium cation 7 and a byproduct 9 containing a phosphairidocenium moiety could be determined by X-ray diffraction.

Cationic allyl palladium complexes of the diasteriomerically pure P-chiral ligand tert-butyl(menthyl-O)phenylphosphinite 1 were prepared from [(η3-C3H5)PdI]2 and [(η3-C3H5)Pd(cod)]X. Ligand 1 and the complex [(η3-C3H5)PdI(1)] 9 were characterized by X-ray crystallography. The absolute configuration at the phosphorus center of 1 was determined to be (S) for the (−)-menthol derivative. Crystals are orthorombic, space group P212121, a=8.505(3) A, b=10.82(1) A, c=23.297(3) A, V=2144(2) A3. Complex 9 shows distorted square planar geometry. Crystals are trigonal, space group P32, a=13.980(5) A, c=11.292(3) A, V=1911(2) A3. Asymmetric codimerization of styrene and ethylene was successfully applied. High enantioselectivities of up to 86% ee have been obtained at room temperature. The codimer 3-phenylbut-1-ene (3PB1) was formed in high selectivity (up to 96%) with only small amounts of the isomerization products E- and Z-2-phenylbut-2-ene. By addition of various coordinating solvents, the catalyst system was efficiently stabilized. Variation of the complex counter anion had significant effect on enantioselectivity.

The new α,ω[phosphanyl(organyl)]borane Me2PCH2B(NMe2)2 (8) was obtained in good yield by the reaction of ClB(NMe2)2 with LiCH2PMe2. Compound 8 forms the transition metal complexes [(CO)5Cr{Me2PCH2(NMe2)2}] (9), [(MeC5H4)Mn(CO)2{Me2PCH2B(NMe2)2}] (10), and [(CO)4Fe{Me2PCH2B(NMc2)2}] (11). which were isolated as highly volatile liquids in high yields. Complex 11 easily underwent exchange reactions of the Me2N substituents which led to derivatives with threefold coordinated boron such as [(CO)4Fe{Me2PCH2B(OMe)2}] (13), and [(CO)4Fe{Me2PCH2B(NMe2)Cl}] (14), or to a compound with tetrafold coordinated boron, [(CO)4Fe{Me2PCH2BCl2(NHMe2)}] (15). Li[(CO)4Fe(Me2PCH2BH3)] (16), cis,trans-[{(CO)4Fe(Me2PCH2BH2)}2] (17), and [(CO)4Fe{Me2PCH2BH2(2,4,6-Me3C5H2N)}] (18) were obtained from 13 by corresponding substitution of the MeO groups. The addition of HSiPh3 to the iron center was achieved by photolysis of 13, giving [(CO)3FeH(SiPh3){Me2PCH2B(OMe)2}] (19). [(CO)5Cr{Me2PCH2B(OMe)2}] (12), the chromium analogue of 13, was obtained from the reaction of [(CO)5Cr{Me2PCH2B(NMe2)2}] (9) with MeOH. The structure of compound 19 was determined by single crystal X-ray diffraction.

A new convenient synthesis for the anionic manganese complex [(C5H4Me)MnH(CO)2]− (1b), from [(C5H4Me)MnH(SiMePh2)(CO)2] and K[BEt3H] is described. Compound 1b which can be isolated on a 15g scale, serves as starting material for the improved syntheses of the borylene complexes [{(C5H4Me)Mn(CO)2}2BR] (2a, b; R = Me2N, Me3C), which are formed in a stiochiometric reaction in good yields. In addition, we report on the synthesis and structure of the salt like compound [{(Me3Si)2N}BH(tmeda)] [{(C5H4Me)Mn(CO)2}2H] (3) showing a Mn-H-Mn unit in solution and in the crystal, which was obtained from the reaction of 1b with [(Me3Si)2N]BCl2.

[PtCl2(S,S-skewphos)] reacts with Me3SiCHN2 in dry CH2Cl2 to give [PtCl(S-CHClSiMe3)(S,S- skewphos)] in high yield, but in the presence of water [Pt(CH2Cl)2)(S,S-skewphos)] is formed. Treatment of [PtCl(S- CHClSiMe3)(S,S-skewphos)] with NaI gives [PtI(CHISiMe3)(S,S-skewphos)] as a 1:1 mixture of diastereoisomers.

Reaction of the 3,4-diboratafulvene deriv. Li2[CH2C[CHB(NEt2)]2] (I) with [RhCl(COD)]2 (COD = cyclooctadiene) gives m-[1-5-h5:1,2,5,6-h4-[CH2C[CHB(NEt2)]2]][Rh(h-COD)]2 (II), the first 3,4-diborafulvene complex which possesses a doubly-opened triple-decker structure with a bridging 3,4-diborafulvene ligand. The crystal structure of II was detd. I serves as a gallium nitride precursor.

Olefin metallation provides an efficient route to novel unsaturated boracarbocycles. Thus the first 3,7-dimethylene-1,5-diboracyclooctanes R 2 NB[CH 2 C(CH 2 )CH 2 ] 2 BNR 2 (R = Et, i Pr) and the first 3,4-dimethyleneboracyclopentanes CH 2 C(Ch 2 )C(Ch 2 )CH 2 B NR 2 (R = Et, i Pr) have been made by treatment of dichloro(dialkylamino)boranes with [Li(TMEDA)] 2 [C(Ch 2 ) 3 and K 2 [( 2 (CH 2 ) 4 ], respectively.