Hans-Friedrich Klein

ortho-Metalation of Triarylphosphane at Cobalt and Template Synthesis of Chelating 2-(Diarylphosphanyl)aroyl Ligands

Elimination of methane from thermally labile CoMe(PPh3)(PMe3)3 generates ortho-metalated Co(2-Ph2PC6H4)(PMe3)3 (1). Addition of dihydrogen causes ring-opening which is followed by a ligand dismutation reaction giving CoH(PMe3)4 and CoH(PMe3)2(PPh3)2. The system does not catalytically hydrogenate olefins. CO insertion into the Co−C bond of 1 results in ring expansion and constitutes a template synthesis of the anionic 2-phosphanylbenzoyl chelate ligand as shown in the molecular structure of Co(2-Ph2PC6H4CO)(CO)(PMe3)2 (3). Oxidative addition of iodomethane transforms 1 into diamagnetic CoMeI(2-Ph2PC6H4)(PMe3)2 (7), while benzoyl chloride oxidizes 1 to paramagnetic CoCl(2-Ph2PC6H4)(PMe3)2 (8). The preservation of the four-membered metallacycle in three successive oxidation states is supported by single-crystal X-ray analyses of 1, 7, and 8.

Steric Control of Cyclometallation Reactions in Schiff-Base Complexes of Cobalt(I) Containing an Anchoring Diphenylphosphanyl Group

2-(Diphenylphosphanyl)alkyliminobenzaldehydes(2-Ph2PC6H4CHNR) react with [CoCH3(PMe3)4] forming five-membered metallacycles in complexes [(2-Ph2PC6H4CNR-C,P)Co(PMe3)3] [1: R = C2H5, 2: R = CH(CH3)2, 3: R = cyclo-C6H11] while the ortho-metallation pathway is selectively followed in the formation of [{2-Ph2PC6H3(CHNR)-C1,P}Co(PMe3)3] [4: R = C(CH3)3]. The presence of a four-membered cobaltocycle in the molecular structure of 4 was confirmed by X-ray analysis. Carbonylation of 2 and 3 gives the monocarbonyl derivatives [(2-Ph2PC6H4CNR-C,P)Co(CO)(PMe3)2] [5: R = CH(CH3)2, 6: R = cyclo-C6H11] while 4 undergoes ring expansion by insertion forming [{2-Ph2PC6H3(CHNR)CO-C,P}Co(CO)(PMe3)2] [7: R = C(CH3)3]. Monosubstitution occurs under 1 bar of ethene giving the π-ethene complexes [(2-Ph2PC6H4CNR-C,P)Co(C2H4)(PMe3)2] [8: R = CH(CH3)2, 9: R = cyclo-C6H11] and [{2-Ph2PC6H3(CHNR)-C1,P}Co(C2H4)(PMe3)2] [10: R = C(CH3)3]. The molecular structure of 9 shows an equatorial π-ethene ligand. Iodomethane oxidizes 2 and 3 to afford the cobalt(II) complexes [(2-Ph2PC6H4CNR-C,P)CoI(PMe3)2] [11: R = CH(CH3)2, 12: R = cyclo-C6H11] and oxidatively adds to 4 to give mer-trans-[{2-Ph2PC6H3(CHNR)-C1,P}CoI(CH3)(PMe3)2] [13: R = C(CH3)3]. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Cobalt induced tandem C-H activation/decarbonylation of various aromatic aldehydes and related benzylic alcohols forming mononuclear aryl monocarbonyl complexes.

Reactions between Co(CH(3))(PMe(3))(4) and various ortho-substituted aromatic aldehydes (Ar(R(1),R(2))CHO) and related benzylic alcohols (Ar(R(1),R(2))CH(2)OH) proceed with high selectivity to give the mono carbonyl complexes Aryl(R(1),R(2))(PMe(3))(3)Co(CO): R(1) = H, R(2) = CH(3) (1), R(1)= H, R(2) = ethyl (2), R(1) = CH(3), R(2) = CH(3) (3), R(1) = H, R(2) = NH(2) (4), R(1) = F, R(2) = F (5), R(1) = H, R(2) = CF(3) (6), and R(1) = H, R(2) = benzo (7). This tandem C-H bond activation/decarbonylation reaction provides easy and rapid access under mild conditions (-70 degrees C) to the first isolated trimethylphosphine stabilized aryl-monocarbonyl complexes of cobalt. X-ray diffraction studies were performed on ortho-amino substituted complex 4, ortho-trifluormethyl 6, and naphthyl derivative 7.

Meridional bicyclometalation with iron: a novel way of forming dianionic [C,N,C]-ligands

Bicyclometalation of aromatic substrates containing imine anchoring groups is achieved with a dimethyliron complex at -70 degrees C; azadiene systems undergo a regiospecific activation of 1,4-CH/N interchanged C-H bonds which may be aromatic or vinylic.

Unexpected formation of a molecular tetraalkyl nickel complex from an olefin/nickel(0) system.

According to the first described method nickel can be brought to its highest oxidation state + 4 by fluorination under strictly anhydrous conditions. Such conditions are essential because salts with the anion [NiF6] 2 undergo hydrolysis and generate dioxygen. During the synthesis the oxidizing power is transferred from the reagent to the metal (low-spin d) that resides in the center of a regular octahedron of six fluoride ions. Within the last fifteen years several Ni compounds have been reported that deviate from this concept in two directions: instead of the hard fluoride donors they contain soft donor atoms, and in addition to coordinatively saturated octahedral Ni centers also coordinatively unsaturated four-coordinate species with only 14 metal-valence electrons are observed. Going much further back we can trace a parallel development for the heavier homologues of nickel. As Pd and Pt adopt higher oxidation states more easily than nickel and are less prone to elimination reactions, thermally stable [C6F5Pd ] compounds became accessible some 30 years ago. Stable aryl palladium(IV) complexes without fluoride substitution could only recently be synthesized and structurally characterized. All the alkyl palladium(IV) halides that have been investigated to date spontaneously decompose above 20 8C. In contrast, the thermally robust and air-stable [Me3PtI] [5] has been known since the beginnings of organometallic chemistry, when in many laboratories the then novel Grignard reagents were first treated with salts of transition elements. Today organoplatinum chemistry is a vast area and includes a large number of tetrameric trimethylplatinum(IV) compounds that have a common fac-octahedal coordination of the metal and a structure motive from a Pt4X4-cubane skeleton (X = F–I, OH, SR, etc.). With this background in mind nobody would have expected that thermally stable alkyl nickel(IV) compounds could be generated. For the series of structurally characterized examples of Ni complexes with coordination numbers six and four, it is interesting to note the modification by degrees in the strength of oxidizing agents required for the synthesis. Octahedral methyl nickel compounds 1 that owe their stability to a favorable balance of trans influences are generated by an oxidative substitution reaction with methyl halide (X = Br, I). For the formation of bis(acylphenolato)nickel 2 and similarly for the homoleptic anion 5 a disproportionation reaction at the Ni stage is sufficient, while the silyl nickel compound 3 is generated by a thermally induced elimination of dihydrogen. In a similar modification for the synthesis of the distorted tetrahedral norbornyl nickel 4 oxidation by air at 60 8C is sufficient. The most recent example, the tetraalkyl 6, appears to arise slowly but spontaneously at ambient conditions from an olefin/Ni system. However, the balance of oxidation–reduction equivalents and the mode of formation are still subject to speculation. [*] Prof. Dr. H.-F. Klein, Dr. P. Kraikivskii Institute for Inorganic and Physical Chemistry Darmstadt University of Technology Petersenstrasse 18, 64287 Darmstadt (Germany) E-mail: hfklein@ac1.ac.chemie.tu-darmstadt.de [] P.K. is a DAAD-fellow from Irkutsk University, Russia, as part of the “Lomonossov” programme. Highlights

Coordination of ortho and para quinones and oxidation reduction processes in trimethylphosphine complexes of cobalt and nickel

Abstract The ortho-quinones 9,10-phenanthrenequinone, 1,2-naphthoquinone, and 3,5-di-tert-butyl-benzoquinone-1,2 oxidatively substitute trimethylphosphine into Ni(PMe3)4 affording molecular compounds containing chelating dioxo ligands of the catecholate type. Using CoMe(PMe3)4 as a substrate the synthesis was extended to tetrachlorobenzoquinone-1,2 and dibenzoyl with retention of the CoMe group. Formally omitting the methyl group, odd-electron complexes were obtained from Co(cyclopentene)(PMe3)3 by reaction with 9,10-phenanthrenequinone or dibenzoyl. The para-quinones 2,5-di-tert-butyl-benzoquinone-1,4 and 2-tert-butyl-naphthoquinone-5,10 displace two trimethylphosphines in Ni(PMe3)4 to form diene complexes of zerovalent nickel. X-ray crystal structures establish the presence of O:O coordinated catecholato ligands for nickel(II) and cobalt(III) and reveal an η4-diene type quinone ligand coordinated to nickel(0).

Spontaneous formation of trinickel clusters containing μ3-imido bridges from 2-nitrophenols and Ni(PMe3)4

Abstract 2-Nitrophenols ArOH (1: 4-Me, 6-CMe3; 2: 4-CMe3, 6-CMe3; 3: 4-OMe, 6-H) are reduced stepwise by Ni(PMe3)4 to form cluster compounds (4–6) in which four trimethylphosphines and two chelating μ3-imidato-2-phenolato ligands are coordinated to a triangulo-Ni3 core. Initially mononuclear trans-octahedral complexes Ni(OAr)2(OPMe3)2 (7–9) containing O:O-coordinated nitrophenolato ligands are formed and eventually converted to (4–6). Crystal and molecular structures for 4 and 7 are discussed. Cluster degradation of 4 with HCl/ether yields the 2-aminophenol.

The Tetrakis(trimethylphosphine)cobalt Anion

Reduction of paramagnetic L4Co (L = (CH3)3P) (d9) by alkali metals affords salts of L4Co- (d10). These are strong reducing agents, powerful bases and very able nucleophiles. They rapidly exchange three of their phosphine ligands for CO. Their reactions with a variety of inorganic and organic halides are shown to be effectively oxidative additions. From the distinct thermochromic behaviour of these salts both in the solid state and in solution a reversible formation involving different states of solvation is deduced.

Reaction of 2-nitrophenols with high-valent trimethylphosphine complexes of cobalt

Abstract Acylphenolato(hydrido)cobalt(III) complexes Co(η 2 -CO,O)H(PMe 3 ) 3 (CO,O=1-carbonyl-2-oxo-5- tert -butyl-cyclohexendiyl; 1-carbonyl-2-oxo-cyclohexendiyl) by reaction with 2-nitrophenol eliminate dihydrogen and are converted to 2-nitrophenolatocobalt(III) compounds. With the former dianionic ligand an intermediate tris(phosphine) compound 1 containing a η 1 -nitrophenolato group is shown to adopt a meridional configuration in the crystal. In solution a η 2 -nitrophenolato coordination mode is usually attained after dissociation of one of the trimethylphosphines resulting in cis and trans isomers of bis(phosphine) compounds 2 and 3 . bis(Phosphine) complexes 5 – 7 ( cis , trans ) were also obtained from Co(η 2 -CO,O)H(PMe 3 ) 3 (CO,O-1-carbonyl-2-oxo-3,4-benzo-cyclohexendiy1; 1-carbonyl-2-oxo-1,2-diphenyl-ethendiyl) and 2-nitronaphthol. No reduction of nitro groups neither by free PMe 3 nor by excess CoH complex was observed although the corresponding nitrosonaphtholato complexes 8 and 9 were readily formed upon combining Co(η 2 -CO,O)H(PMe 3 ) 3 (CO,O=1-carbonyl-2-oxo-5- tert -butyl-cyclohexendiyl; 1-carbonyl-2-oxo-1,2-diphenyl-ethendiyl) and 2-nitrosonaphthol.

Reduction of 2-Nitrophenols by Low Valent Trimethylphosphine Complexes of Cobalt

2-Nitrophenols [C 6 H 3 R 4 R 6 (NO 2 )OH] react with Co(PMe 3 ) 4 to afford 2-nitrosophenolatocobalt (I) compounds Co[η 2 - N , O ][C 6 H 2 R 4 R 6 (NO)O](PMe 3 ) 3 ( 1 : R 4 =R 6 =H; 2 : R 4 =Me, R 6 =CMe 3 ). In the molecular structure of 2 the cobalt atom is centered in a trigonalbipyramid of axial O , P and equatorial N , P 2 donor atoms, whereas an isosteric molecule Ni[η 2 - C , O ][C 6 H 2 R 4 R 6 (CO)O](PMe 3 ) 3 ( 2C : R 4 =Me, R 6 =CMe 3 ) containing axial C,P and equatorial O,P 2 donor atoms crystallizes in a different space group. From 2-nitronaphthol-1 or 2-nitrosonaphthol-1 and Co(PMe 3 ) 4 a nitrosocobalt(I) complex Co[η 2 - N , O ][C 10 H 6 (NO)O](PMe 3 ) 3 ( 3 ) is obtained. 2-Nitronaphthol-1 reacting with excess Co(PMe 3 ) 4 affords dinuclear compounds Co 2 [η 3 - O ,μ 2 - N ][C 10 H 6 (N)O](PMe 3 ) 5 ( 4 ) and Co 2 {[η 3 - O ,μ 2 - NH ][C 10 H 6 (NH)O]} 2 (PMe 3 ) 4 ( 5 ). The molecular structure of 4 shows a rather long metal to metal bond (CoCo=2.628(1) A) which attains a normal value in that of 5· 2THF (CoCo=2.399(1) A). Reactions of low-valent carbonyl(trimethylphosphine)cobalt complexes with 2-aminophenol afford Co 2 [μ 2 - CO ; η 3 - O ,μ 2 - NH ][C 10 H 6 (NH)O](CO)(PMe 3 ) 4 ( 6 ).