Thomas Lügger

A zwitterionic carbene–stannylene adduct via cleavage of a dibenzotetraazafulvalene by a stannylene

Abstract Reaction of the tetraamine 1,2-C6H4-[NHCH2CH2N(CH3)2]2 (8) with bis(bis(trimethylsilyl)amido)tin(II) yields the N-heterocyclic stannylene 1,2-C6H4-[NCH2CH2N(CH3)2]2Sn (9) which contains additional 2-(dimethylamino)ethyl groups at the nitrogen atoms of the five-membered ring. These additional donor groups provide for an intramolecular stabilization of the electron deficient tin center. The X-ray structure analysis with crystals of 9 shows two three-coordinated tin atoms with different coordination environments in a dinuclear complex. Reaction of the stannylene 9 with the N,N′N′′N′′′-tetramethyldibenzotetraazafulvalene 4 leads via CC bond cleavage in the dibenzotetraazafulvalene to the yellow carbene–stannylene adduct 10. The X-ray structure analysis of 10 reveals bond parameters consistent with a zwitterionic species made up from a partially cationic carbene subunit and a partially anionic stannylene unit.

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).

Platinum(II) and palladium(II) complexes with 1,2-dihydrobenzoxazol-2-ylidene ligands and molecular structure of trans-bis(1,2-dihydrobenzoxazol-2-ylidene) diiodo palladium

Abstract 2-Trimethylsiloxyphenyl isocyanide 1 reacts with [MCl2(NCPh)2] (M = Pd, Pt) to yield homoleptic tetraisocyanide complexes [M(1)4]Cl2. Subsequent hydrolysis of the Si-O bonds leads to intramolecular nucleophilic attack at the isocyanide carbon atom with formation of homoleptic complexes with four 1,2-dihydrobenzoxazol-2-ylidene ligands (M = Pt, X = Cl, 2; M = Pt, X = BF4, 3; M = Pd, X = Cl, 4). Double deprotonation of 4 by ammonia yields the neutral complex 5. Under similar conditions, PdI2 reacts with 1 even in excess to give only the diisocyanide complex trans-[PdI2(1)2] 6 which upon Si-O bond cleavage yields the neutral dicarbene complex trans-bis(1,2-dihydrobenzoxazol-2-ylidene)diiodo palladium 7. Complex 7 was shown by X-ray crystallography to contain a planar tetracoordinated palladium atom and two carbenoid benzoxazole rings which are rotated by about 80° relative to the palladium coordination plane.

Dinuclear Complexes with Bis(benzenedithiolate) Ligands

As a part of a broader study directed towards helical coordination compounds with benzenedithiolate donors, we have synthesized the bis(benzenedithiol) ligands 1,2-bis(2,3-dimercaptobenzamido)ethane (H(4)-1) and 1,2-bis(2,3-dimercaptophenyl)ethane (H(4)-2). Both ligands form dinuclear complexes with Ni(II), Ni(III) and, after air-oxidation, Co(III) ions under equilibrium conditions. Complexes (NEt(4))(4)[Ni(II)(2)(1)(2)] (11 b), (NEt(4))(2)[Ni(III)(2)(1)(2)] (13), and Na(4)[Ni(II)(2)(2)(2)] (14) were characterized by X-ray diffraction. In all complexes, two square-planar [Ni(S(2)C(6)H(3)R)(2)] units are linked in a double-stranded fashion by the carbon backbone and they assume a coplanar arrangement in a stair-like manner. Cyclic voltammetric investigations show a strong dependence of the redox potential on the type of the ligand. The substitution of 1(4-) for 2(4-) on nickel (-785 mV for 11 b versus -1130 mV for 14, relative to ferrocene) affects the redox potential to a similar degree as the substitution of nickel for cobalt (-1160 mV for [Co(2)(1)(2)](2-)/[Co(2)(1)(2)](4-), relative to ferrocene). The redox waves display a markedly less reversible behavior for complexes with the shorter bridged ligand 2(4-) compared to those of 1(4-).

Komplexe des 2-(Trimethylsiloxy)phenylisocyanids als Vorstufen für die Darstellung von N,O-Heterocarben-Komplexen

Abstract The reaction of 2-(trimethylsiloxy)phenylisocyanide 1 with PdI 2 or CoI 2 leads to the square-planar complex trans -[Pd( l ) 2 I 2 ] 2 and the octahedral complex trans -[CO( 1 4 I 2 ] 3 , respectively. Both 2 and 3 were characterized by X-ray structure analysis. Cleavage of the Si-O bond gives complexes with coordinated 2-hydroxyphenylisocyxanide ligands which rearrange via an intramolecular nucleophilic attack of the hydroxyl oxygen at the isocyanide carbon to give complexes with cyclic N,O-heterocarbene ligands.

cis‐Octahedral Nickel(II) Complexes with Symmetric and Unsymmetric Tripodal Tetraamine Ligands

Nickel(II) complexes with the aliphatic tripodal tetraamine ligands N(CH2CH2NH2)3 (tren, 1), N[(CH2CH2CH2NH2)(CH2CH2NH2)2] (baep, 2), N[(CH2CH2CH2NH2)2(CH2CH2NH2)] (abap, 3), and N(CH2CH2CH2NH2)3 (trpn, 4) are reported. The tripodal tetradentate N4 ligands 1−4 react with Ni(NO3)2·6H2O in acetonitrile or methanol to give the blue nickel(II) complexes [Ni(1)(η1-NO3)2] (5a), [Ni(2)(η1-NO3)2] (5b), [Ni(3)(η2-NO3)]NO3·CH3CN (5c·CH3CN), and [Ni(4)(η2-NO3)]NO3·CH3OH (5d·CH3OH). With NiCl2·6H2O, the complexes [Ni(1)Cl(H2O)]Cl·H2O (6a), [Ni(2)(μ-Cl)2Ni(2)]Cl2·2CH3OH (6b·2CH3OH), [Ni(3)Cl(H2O)]Cl (6c), and [Ni(4)(H2O)2]Cl2·H2O (6d·H2O) are obtained. The molecular structures of complexes 5a−d and 6b−d have been determined by X-ray diffraction analysis and they are compared with the molecular structure of the previously characterized complex 6a. Complexes 5a−d and 6b−d exhibit octahedrally coordinated nickel atoms. The tripodal ligands occupy four of the six coordination sites in a pseudo-facial manner. Complexes of the unsymmetrical ligands 2 and 3 possess both five- and six-membered chelate rings. The extension of the ligand arms in 1−4 leads to a systematic variation in the geometric and UV/Vis spectroscopic properties of the complexes depending on the size of the chelate rings formed by the ligands.

Synthesis and structural characterization of molybdenum complexes with linked cycloheptatrienyl-phosphane ligands

Abstract The synthesis of P-functionalized cycloheptatrienyl chelate complexes incorporating the linked cycloheptatrienyl–phosphane ligand [2-(diisopropylphosphanyl)phenyl]cycloheptatrienyl, o-iPr2PC6H4C7H6, is described. The ligand precursor [2-(cyclohepta-2,4,6-trienyl)phenyl]diisopropylphosphane (2b) can be obtained by addition of lithiated 2-BrC6H4PiPr2 (1b) to the tropylium cation C7H7+. On reaction with Mo(CO)6, the P-functionalized cycloheptatriene 2b acts as an eight-electron ligand to afford the cycloheptatriene–phosphane chelate complex [(o-iPr2PC6H4η6-C7H7)Mo(CO)2(PMo)] (3b) as a single, chiral regioisomer, which undergoes clean hydride abstraction on treatment with (Ph3C)BF4. The resulting cationic complex 4b reacts with sodium bromide to yield the ‘chiral-at-metal’ complex [(o-iPr2PC6H4η7-C7H6)Mo(CO)Br(PMo)] (5b). This 18-electron complex can be oxidized with 0.5 equivalent Br2 to give paramagnetic [(o-iPr2PC6H4η7-C7H6)MoBr2(PMo)] (6b). 6b is a versatile starting material for the preparation of various cycloheptatrienyl–molybdenum complexes, which is exemplified by the isolation of the dialkyl complex [(o-iPr2PC6H4η7-C7H6)Mo(CH2SiMe3)2(PMo)] (7b) upon reaction of 6b with Me3SiCH2MgCl. In addition, the X-ray crystal structures of 3b, 4b, 5b, 6b, and 7b are reported.

A new tetranuclear iron complex with a [Fe4O6](6+) core: synthesis, structure, spectroscopic and magnetic properties

Abstract The reaction of 2,6-bis(hydroxymethyl)-4-tert-butylphenol (H3L) with [Fe(III)(acac)3] in acetonitrile in the presence of NEt3 yields [Fe(III)4(HL)6(acac)2](HNEt3)2·3CH3CN (1) or after subsequent addition of [NEt4]Cl [Fe(III)4(HL)6(acac)2](NEt4)2 (2) as reddish-brown crystalline solids. The molecular structure of 1 was established by single crystal X-ray diffraction. The dianion of complex 1 contains an [Fe4O6]6+ core with two μ3-bridging benzylalcoholato ligands and four μ2-bridging benzylalcoholato ligands. This is the first structurally characterized example for a benzylalcoholato ligand bound to an octahedrally coordinated iron ion. The core of 1 can be considered as two face-sharing cuboidal [Fe3O4]5+ units. Compound 2 has been examined by FTIR, UV–Vis–NIR-absorption, 57Fe Mossbauer, and magnetochemical measurements. Compound 2 has an St=0 ground state indicative of antiferromagnetic interactions between the high-spin Fe(III) metal ions. The spin topology resembles that of the known [Fe4O2]8+ core with a ‘butterfly’ disposition of the four iron ions. Fitting of the data to the appropriate spin-Hamiltonian yields exchange-coupling constants between the ‘inner’ (‘body’) iron ions of Jbb=−10.0±0.1 cm−1 and between the ‘inner’ iron ions and ‘outer’ (‘wing-tip’) iron ions of Jwb=−6.2±1.0 cm−1. The differences of the spectroscopic and magnetochemical properties between the [Fe4O6]6+ core and the [Fe4O2]8+ core with an inversion of the superexchange pathways are discussed.

Synthesis and X‐ray Molecular Structure of [WVI(C6H4S2‐1,2)3] Completing the Structural Characterization of the Series [W(C6H4S2‐1,2)3]n− (n = 0, 1, 2): Trigonal‐Prismatic versus Octahedral Coordination in Tris(benzene‐1,2‐dithiolato) Complexes

The tris(benzene-1,2-dithiolato) complex [WVI(C6H4S2-1,2)3] 1 was synthesized from [W(CH3)6] and C6H4(SH)2-1,2 in diethyl ether. Crystals of [WVI(C6H4S2-1,2)3] were obtained from a saturated dichloromethane solution at room temperature. The X-ray crystal structure analysis revealed that the tungsten atom in 1 is coordinated in an almost perfect trigonal-prismatic fashion with W−S distances between 2.3724(14) A and 2.3840(14) A.

Chelate Complexes of Functionalized Cycloheptatrienyl Ligands: 17‐ and 18‐Electron Molybdenum Complexes with Linked Cycloheptatrienyl−Phosphane Ligands and Their Use in Transition Metal Catalysis

The synthesis of P-functionalized molybdenum chelate complexes incorporating the linked cycloheptatrienyl− phosphane ligand [2-(diphenylphosphanyl)phenyl]cycloheptatrienyl, o-Ph2P−C6H4−C7H6, is described. The air-stable ligand precursor [2-(cyclohepta-2,4,6-trienyl)phenyl]diphenylphosphane (2) can be obtained in large quantities by addition of lithiated 2-BrC6H4PPh2 (1) to the tropylium cation C7H7+. Hydride abstraction employing the trityl cation, Ph3C+, results in the formation of the tricyclic phosphonium salt 3. The P-functionalized cycloheptatriene 2 acts as an eight-electron ligand on reaction with Mo(CO)6 to afford the cycloheptatriene−phosphane complex [(o-Ph2PC6H4-η6-C7H7)Mo(CO)2(P−Mo)] (4) as a single, chiral regioisomer, which undergoes clean hydride abstraction on treatment with (Ph3C)BF4. The resulting cationic cycloheptatrienyl−phosphane complex 5 reacts with sodium bromide to yield the uncharged “chiral-at-metal” complex [(o-Ph2PC6H4-η7-C7H6)Mo(CO)Br(P−Mo)] (6). This 18-electron complex can be oxidized with 0.5 equiv. of Br2 to give the paramagnetic dibromo complex 7, which is a versatile starting material for the preparation of the 17-electron mono- and dialkyl complexes [(o-Ph2PC6H4-η7-C7H6)Mo(CH2SiMe3)X(P−Mo)] (X = Br, 8; X = CH2SiMe3, 9). In combination with Me3SiCH2MgCl, complexes 7 and 9 prove to be active catalysts for the ring-opening metathesis polymerization of norbornene. In addition, the X-ray crystal structures of 2, 4, 5·CH2Cl2, 7·CHCl3, 8, and 9·C6H14 are reported.