F. Ekkehardt Hahn

Palladium complexes with bridged and unbridged benzimidazolin-2-ylidene ligands

Abstract Two equivalents of N , N ′-dimethylbenzimidazolyl iodide ( 1 ) react with Pd(OAc) 2 to yield the complex cis -bis( N , N ′-dimethyl-benzimidazoli-2-ylidene)diiodo palladium ( 2 ). The potentially bidentate ligand 1,1′-methylene-bis( N -methylbenzimidazolyl) diiodide ( 3 ) reacts with Pd(OAc) 2 to yield the complex [1,1-methylene-bis( N -methylbenzimidazolin-2-ylidene)]diiodo palladium ( 4 ) with a bidentate carbene ligand. Both complexes were characterised by 1 H- and 13 C-NMR spectroscopy. The X-ray crystal structures of 2 and 4 reveal that methylene-bridging of the benzimidazolin-2-ylidene ligands leads to palladium complexes with a reduced C carbene –Pd–C carbene angle (91.3(2) in 2 vs. 83.7(3)° in 4 ). In addition, the angles between the planes of the carbene ligands and the PdC 2 I 2 plane are reduced from almost perpendicular in 2 (83.06(10) and 79.84(13)°) to 54.4(2) and 51.8(2)° in 4 , while comparable bond distances in 2 and 4 are identical within experimental error.

Synthesis and reactions of trigonal-bipyramidal rhenium and technetium complexes with a tripodal, tetradentate NS3 ligand

Neutral, trigonal-bipyramidal complexes of technetium and rhenium with the tripodal, tetradentate ligand 2,2′,2″-nitrilotris(ethanethiol), N(CH2CH2SH)3 (H31) have been synthesized and characterized. The technetium complex [99Tc(1) (PPh3)] (2) can be obtained by reduction of K99TcO4 with PPh3 in the presence of H31 or by substitution reaction starting from [99TcCl3(PPh3)2(NCMe)]. The trigonal-bipyramidal complex 2, C24H27NPS3Tc, crystallizes in the monoclinic space group P21/c with a=8.906(2), b=25.804(6), c=11.061(4) A, β=108.42(2)° and Z=4. Rhenium complexes [Re(1) (PR3)] (3) (PR3 = PPh3 (3a, PMe2Ph (3b), PMePH2 (3c), P(n-Bu)3 (3d), P(OEt)3 3e)) have been obtained in analogy to the technetium derivative 2 by reduction of NH4ReO4 with phosphines PR3 in the presence of H31. Complex 3a, C24H27NPReS3, crystallizes in the monoclinic space group P21/n with a=10.855(3), b=16.707(4), c=15.441(5) A, β=92.62(2)° and Z=4. Rhenium complexes containing an isocyanideco-ligand [Re(1) (CNR)] (5) (R=CH2COOMe (5a), t-Bu (5b), Ph (5c), CH2CH2NC4H8O (5d), CH2COOEt (5e)) aan be prepared by substitution of the phosphine ligand in 3 for an isocyanide or by reaction of the isocyanide complexes [ReCl3(PPh3)2(CNR)] (4) (R=CH2COOMe (4a), t-Bu (4b), Ph (4c), CH2CH2NC4H8O (4d)) with H31. The crystal structure of complex 4b has been determined. 4b crystallizes with one molecule of CH2Cl2 per formula unit. Crystals of 4b·CH2Cl2, C42H41Cl5NP2Re, are monoclinic, space group P21/c with a=12.868(3), b=20.454(7), c=16.378(9) A, β=104.71(4)° and Z=4. The substitution reaction starting with complexes of type 3 gives the best yields in the preparation of complexes of type 5. Two complexes of the type [Re(1) (CNR)] were characterized by X-ray crystallography. Crystals of 5a, C10H17N2O2ReS3, are monoclinic, space group P21/c with a=7.827(4), b=13.866(3), c=13.627(6) A, β=93.19(7)° and Z=4. Crystals of 5b, C11H21N2ReS3, are monoclinic, space group P21/c with a=12.084(2), b=11.915(2), c=12.244(3) A, β=114.31(2)° and Z=4. Treatment of 5e with LiOH leads to ester hydrolysis and yields the complex [Re(1) (CNCH2COOH)] (6) while reaction of 5d–5e in the two-phase system toluene/conc. hydrochloric acid gives the carbonyl complex [Re(1) (CO)] (7) which was characterized by X-ray crystallography. Crystals of 7, C7H12NOReS3, are triclinic, space group P1 with a=7.924(2), b=10.467(3), c=13.556(2) A, α=96.61(2), β=90.47(2), γ=101.68(2)° and Z=4 (2 molecules of 7 per asymmetric unit).

Pentacarbonylchromium(0) and -tungsten(0) complexes with the bis(diisopropylamino) cyclopropenylidene ligand

Bis(diisopropylamino)cyclopropenylidene (1a) generated by deprotonation of the cyclopropenylium salt (5) with n-butyllithium reacts with [(thf)M(CO)5] (M ue5fb Cr, W) to form the carbene complexes [(1a)Cr(CO)5] (6a) and [(1a)W(CO)5] (6b). The X-ray crystal structure of 6b is reported. Spectral and structural data of 6a and 6b are compared to other [(carbene)M(CO)5] complexes, confirming 1a to be strong donor ligand.

Synthesis of N-allyl-2,3-dihydrobenzoxazol-2-ylidene complexes of chromium(0) and tungsten(0)

Abstract The reaction of 2-trimethylsiloxyphenyl isocyanide ( 1 ) with [M(CO) 5 (THF)] (M=Cr, W) gives the complexes [M(2-Me 3 SiO–C 6 H 4 NC)(CO) 5 ] ( 2 ) ( 2a , M=Cr; 2b , M=W). Hydrolysis of the Si–O bond leads to the formation of an equilibrium between complexes 3 ( 3a , M=Cr; 3b , M=W) with a 2-hydroxyphenyl isocyanide and complexes 4 ( 4a , M=Cr; 4b , M=W) with a 2,3-dihydrobenzoxazol-2-ylidene ligand. Deprotonation of mixtures 3 / 4 followed by alkylation with allyl bromide yields exclusively N -allyl-2,3-dihydrobenzoxazol-2-ylidene complexes ( 5 ) ( 5a , M=Cr; 5b , M=W). Thermally induced intramolecular substitution of one cis -carbonyl ligand in ( N -allyl-2,3-dihydrobenzoxazol-2-ylidene)-pentacarbonyltungsten ( 5b ) results in the formation of the alkene–carbene complex 6 incorporating an η 2 :η 1 -( N -allyl-2,3-dihydrobenzoxazol-2-ylidene) ligand. The molecular structure of 5b is reported.

Synthesis and characterization of isocyanide containing rhenium(III) complexes trans-[ReCl3(CNR)(PPh3)2] and crystal structure of trans-[ReCl3(CN-t-C4H9)(PPh3)2]

Abstract Isocyanide containing complexes trans-[ReCl3(CNR)(PPh3)2] (3) (R = tert-C4H9 (3a), c-C6H11 (3b, C6H5 (3c), CH2C(O)OCH3 (3d), CH2CH2-(N-morpholinyl) (3e)) were obtained by reduction of trans-[Re(O)Cl3(PPh3)2] with an excess of triphenylphosphane in the presence of the isocyanide or by substitution of the acetonitrile ligand in trans-[ReCl3(NCCH3)(PPh3)2] by the isocyanide ligand. Generally, the substitution reaction starting with Re(III) gives a higher yield. The crystal structure of 3a has been determined by X-ray diffraction methods, 3a crystallizes with one molecule of CH2Cl2 per formula unit. Crystals of 3a·CH2Cl2 are monoclinic, space group P2 1 /c with a = 12.868(3), b = 20.454(7), c = 16.378(9) A , β = 104.71(4)°, Z = 4 and D o - 1.58 g cm −3 . The structure was solved from 6190 diffraction data colletced at − 100(2) °C and refined to R = 0.0429 (Rw = 0.0727).

Synthesis of trichlorooxo-bis(2,6-dimethylphenylisocyanide) rhenium(V) and crystal structure of μ-oxo-bis[dichlorooxo-bis(2,6-dimethylphenylisocyanide) dirhenium(V)]

The rhenium diisocyanide complex fac -[Re(O)Cl 3 (CNC 6 H 3 -(CH 3 ) 2 -2,6) 2 ] ( 1 ) was obtained by reaction of mer -[Re(O)Cl 3 (SMe 2 )-(OPPh 3 )] with 2 equiv. of the ligand 2,6-dimethylphenylisocyanide. In the presence of water complex 1 reacts under HCl evolution to yield [(2,6-(CH 3 ) 2 -C 6 H 3 NC) 2 Cl 2 (O)Re O Re(O)Cl 2 (CNC 6 H 3 -(CH 3 ) 2 -2,6) 2 ] ( 2 ). The dinuclear complex 2 was shown by X-ray crystallography to contain an almost linear O Re O Re O core. Crystals of 2 , C 36 H 36 Cl 4 N 4 O 3 Re 2 , are orthorhombic, space group Pccn (No. 56) with a = 11.169(9), b = 13.761(4), c = 25.831(6)A, Z = 4 and D c = 1.818g cm −3 .

Formation of a rhenium(III) carbonyl complex by electrophilic attack on rhenium isocyanides. Synthesis and molecular structure of {Re[N(CH2CH2S) 3][CNC(CH3) 3]} and {Re[N(CH2CH2) 3](CO)}

Abstract Treatment of the trigonal-bipyramidal complex {Re[N(CH 2 CH 2 S) 3 ](CNCH 2 COOEt)} ( 1a ) with LiOH in THF leads to ester hydrolysis and yields the complex {Re[N(CH 2 CH 2 S) 3 ](CNCH 2 COOH)} ( 2 ). Attempts to hydrolyze the ester in 1a in the two-phase system toluene/concentrated hydrochloric acid proceeded under electrophilic attack at the isocyanide nitrogen atom and formation of the carbonyl complex {Re[N(CH 2 CH 2 S) 3 ](CO)} ( 3 ). Complex 3 was also obtained by treatment of {Re[N(CH 2 CH 2 S) 3 ][CNC(CH 3 ) 3 ]} ( 1b ) with toluene/hydrochloric acid. The molecular structures of 1b and 3 were established by X-ray structure analysis.

Isocyanide complexes of titanium: Synthesis and X-ray crystal structure of cis-tetrachlorobis(2-trimethylsiloxyphenylisocyanide) titanium(IV)

Abstract The reaction of TiCl 4 with 2-trimethylsiloxyphenyl isocyanide 1 is described. At −10 °C reaction of TiCl 4 with 1 in n -hexane yields the air-sensitive octahedral diisocyanide complex cis -[TiCl 4 ( 1 ) 2 ] 2 . This complex crystallizes from n-hexane as solvate 2 · C 6 H 14 and was characterized by X-ray crystallography. At room temperature TiCl 4 reacts with 1 in toluene to give an orange air-sensitive compound 3 , which was not completely characterized. Elemental analyses indicate the formation of a complex composed of one molecule of TiCl 4 and one molecule of 1 . IR spectroscopy shows that no isocyanide ligand is present in 3 .

Chelate complexes of cobalt(III) with bis(dithiolate) ligands: backbone influence on the electronic properties and the reactivity of the metal center

The tetradentate bis(dithiolate) ligands 1,4-bis[(2,3-disulfanylbenzamido)methyl]benzene H4L1 and 1,7-bis(2,3-disulfanylbenzamido)heptane H4L2 were prepared and converted into the dinuclear titanocene complexes [(TiCp2)2(L1)] 1 and [(TiCp2)2(L2)] 2, respectively. A ligand transfer reaction of 1 and 2 with [NR4]2[CoCl4] (Rxa0=xa0Et or Me) led to the formation of the bis(dithiolato)cobaltate(III) complexes [NEt4][Co(L1)] 3 and [NR4][Co(L2] (Rxa0=xa0Et 4a or Me 4b). The anion [Co(L2)]– adopts an approximately square-planar co-ordination geometry. Two anions are connected by intermolecular Co–S contacts at the apical position of the metal to form [Co(L2)]22–. In contrast, mononuclear 3 turned out to be unstable with respect to its co-ordination polymer. This phenomenological difference between 3 and 4a, 4b is reflected in the UV-VIS and cyclic voltammetry data of the complexes, which are compared to the data of the corresponding prototype complex tetraethylammonium [bis(3-N-benzylcarbamoylbenzene-1,2-dithiolato)cobaltate(III)] 5 with two unbridged dithiolato-ligands (L3)2–.

PREPARATION AND CRYSTAL STRUCTURES OF A BIDENTATE ISOCYANIDE AND ITS TETRACARBONYLCHROMIUM COMPLEX

Abstract The bidentate diisocyanide ligand 2,2′-(methylendioxy)diphenylisocyanide 4 was prepared by Williamson coupling of 2 with dichloromethane, reduction of the nitro functions and conversion ofthe primary amine groups into isocyanide function Ugi synthesis. The novel ligand 4 reacts with [M(nor)(CO)4] (nor = norbornadiene) to yield the complexes [M(4)(CO)4] ( M = Cr , 5 ; M = Mo , 6 ) which possess 12-membered chelate rings, the smallest rings observed so far for chelating isocyanide ligands. Compounds 4 and 5 were characterized by X-ray crystallography.