Christopher G. Howard

t-Butyl isocyanide complexes of rhenium(I), chromium(O), tungsten(O,I) and platinum(II); X-ray crystal structures of bis(t-butylisocyanide)- tris(trimethylphosphine)chlororhenium(I) and tris(t-butylisocyanide)bis(trimethyl- phosphine)chlororhenium(I)

Abstract The reduction of ReCl 4 (THF) 2 in the presence of excess t -butylisocyanide by sodium amalgam produces pentakis ( t -butylisocyanide)chlororhenium(I), which has been converted to the corresponding methyl and ethyl derivatives. The reaction of pentakis(trimethylphosphine)chlororhenium(I) with Bu t NC gives partially substituted complexes, ReCl(CNBu t ) 2 (PMe 3 ) 3 and ReCl(CNBu t ) 3 (PMe 3 ) 2 . The structures of both compounds have been determined by X-ray methods. Octahedral ReCl(CNBu t ) 2 (PMe 3 ) 3 has trans isocyanide groups with one linear [C N C = 175(1)°] and one slightly bent [C N C = 159(1)°]. The Re C bond lengths are equal within experimental error [2.004(7), 2.003(7)A]. In the octahedral ReCl(CNBu t ) 3 (PMe 3 ) 2 , for which the structure is not well defined, due to disorder, the unique isocyanide trans to chlorine is considerably bent at the nitrogen atom [C Nˆ C = 141(6)°] and appears to show the shortest Re C bond length, 1.94(5) vs 2.02(5)Afor the other two isocyanides which are mutually trans . Protonation of these two isocyanide complexes with fluoroboric acid gives, respectively, the salts [ReCl(CNBu t )CNHBu t (PMe 3 ) 3 ]BF 4 and [ReCl(CNBu t ) 2 CNHBu t (PMe 3 ) 2 ]BF 4 , whose configurations have been determined by NMR spectroscopy. The reduction by sodium amalgam of Cr 2 (CO 2 Me) 4 in tetrahydrofuran in presence of Bu t NC gives a high yield of Cr(CNBu t ) 6 while similar reduction of the dimeric tungsten(II) complex of the anion (mhp) of 2-methyl-6- hydroxypyridine gives W(CNBu t ) 6 . Interaction of W 2 (mhp) 4 in methanol-ether with Bu t NC gives a tungsten(I) complex W 2 (η-mhp) 2 (Bu t NC) 4 , which may be an intermediate in the reductive cleavage reaction. Interaction of cis -PtMe 2 (PMe 3 ) 2 with Bu t NC leads only to replacement of one PMe 3 group to give the complex cis -PtMe 2 (PMe 3 )(CNBu t ).

Alkyl, hydrido, and tetrahydroaluminato complexes of manganese with 1,2-bis(dimethylphosphino)ethane (dmpe). X-Ray crystal structures of Mn2(µ-C6H11)2(C6H11)2(µ-dmpe), (dmpe)2Mn(µ-H)2AlH(µ-H)2AlH(µ-H)2-Mn(dmpe)2, and Li4{MnH(C2H4)[CH2(Me)PCH2CH2PMe2]2}2·2Et2O

Alkylation of MnBr2dmpe)2[dmpe = 1,2-bis(dimethylphosphino)ethane] with MgBut2 leads to the t-butyl complex MnBut2(dmpe); alkylation with Mg(C6H11)2 gives the cyclohexyl-bridged dimer Mn2(µ-C6H11)2(C6H11)2(µ-dmpe)(2). By contrast, alkylation with MgEt2 leads to the diamagnetic manganese(I) species, trans-MnH (C2H4)(dmpe)2. Interaction of the latter with LiBut leads to deprotonation of the dmpe ligand and formation of a complex, (4), of stoicheiometry Li2(MnH(C2H4)[CH2(Me)PCH2CH2PMe2]2}·Et2O. A reduction of MnII to MnI also occurs in the interaction of MnBr2(dmpe)2 with LiAlH4 when the tetrahydroaluminate complex [Mn(AlH4)(dmpe)2]2(5) is formed. Hydrolysis of (5) gives the volatile diamagnetic hydride MnH3(dmpe)2. The X-ray crystal structures of the complexes (2), (4), and (5) have been determined. In (2), the molecule, which has two-fold symmetry, has two manganese atoms each bound to one terminal related cyclohexyl group [Mn–C = 2.118(10)A] and bridged asymmetrically by two symmetry related cyclohexyls [Mn–C = 2.256(9), 2.327(9)A]. The Mn ⋯ Mn distance is quite short at 2.616(5)A and the manganese atoms have a distorted tetrahedral co-ordination. In complex (4), two MnH(C2H4)(dmpe)2 units [Mn–H 1.44(4),Mn–C (av.) 2.121(5), Mn–P 2.213(3)–2.274(3)A] have each lost two hydrogen atoms, one from each of two dmpe methyls, and the resulting four CH2 groups form multicentre alkyl bridges to a central Li4 tetrahedron [C ⋯ Li 2.20–2.36(I), Li ⋯ Li 2.46(1)–2.69(1)A]. Two of the lithiums are co-ordinated by diethyl ether [ Li–O 2.053(8)A]. The complex as a whole has C2 symmetry and the manganese(I) centre has a pseudo-octahedral geometry, although pentagonal bipyramidal is an alternative description if the ethylene is considered to occupy two co-ordination sites. Complex (5) is a centrosymmetric dimer in which two cis-octahedral MnH2(dmpe)2 units are bridged by a AlH-(µ-H)2AlH moiety via Al(µ-H)2Mn linkages. The two H atoms in the AlH2Mn bridge are closer to the Mn atoms [Mn–H = 1.61(3), 1.63(3)A] than to the Al atoms [Al–H = 1.81(3), 1.81(3)A]. The Al–H distances in the AlH2Al unit are 1.64(3) and 1.80(3)A, while the terminal Al–H distance is 1.51(3)A. The aluminium has trigonal bipyramidal co-ordination with one terminal hydrogen in an equatorial position.

Tertiary phosphine adducts of manganese(II) dialkyls: synthesis and X-ray crystal structure of bis(trimethylphosphine)bis(trimethylsilylmethyl)bis(µ-trimethylsilylmethyl)dimanganese(II)

The interaction of PMe3 with [Mn(CH2SiMe3)2]n gives Mn2(CH2SiMe3)4(PMe3)2, the frist crystallographically characterised unidentate phosphine complex of manganese(II).

Tertiary phosphine adducts of manganese(II) dialkyls. Part 2. Synthesis, properties, and structures of monomeric complexes

Monomeric tetrahedral manganese dialkyl tertiary phosphine complexes of stoicheiometry MnR2(PR′3)2 have been identified in solutions by electron spin resonance spectra and the alkyl complex Mn(CH2CMe2Ph)2(PMe3)2 isolated and structurally characterised by X-ray crystallography. The molecule has a severely distorted tetrahedral geometry with P–Mn–P and C–Mn–C angles of 96.2 and 137.9° respectively, which reflect the relative sizes of the two kinds of ligand. The Mn–C and Mn–P distances are 2.149(6) and 2.633(4)A respectively. Use of the chelating phosphine, 1,2-bis(dimethylphosphino)ethane (dmpe), has allowed the isolation of the tetrahedral monomers MnR2(dmpe)(R = CH2SiMe3, CH2CMe3, and CH2Ph). The chelate dialkyl o-xylylene, o-(CH2)2C6H4, gives an octahedral complex Mn[o-(CH2)2C6H4](dmpe)2 whose structure has also been determined by X-ray diffraction. In this molecule, all metal-ligand bond lengths are shorter than the corresponding bonds in Mn(CH2CMe2Ph)2(PMe3)2. This is consistent with a significant reduction in the MnII radius on adoption of the low-spin state observed. The Mn–C distances are 2.110(5) and 2.1 04(6)A, while the Mn–P distances of 2.230(3)(trans to P) and 2.298(3)A(trans to C) reflect the different trans-influence abilities of alkyls and phosphines. The X-band e.s.r. spectra of the monomeric complexes have been studied in detail and are discussed in terms of distorted tetrahedral high-spin MnII and octahedral low-spin MnII species.

Tertiary phosphine adducts of manganese(II) dialkyls. Part 1. Synthesis, properties and structures of alkyl-bridged dimers

The reactions of manganese(II) dialkyls with tertiary phosphines or of MnCl2 with magnesium dialkyls in the presence of phosphines leads to dimeric complexes of stoicheiometry Mn2R4(PMe3)2(R = CH2SiMe3, CH2CMe3, and CH2Ph) and Mn2(CH2SiMe3)4(PR3)2[R3= Et3, Me2Ph, McPh2, and (cyclo-C6H11)3]. The X-ray crystal structures of Mn2(CH2CMe3)4(PMe3)2, Mn2(CH2Ph)4(PMe3)2, and Mn2(CH2SiMe3)4(PMePh2)2 have been determined. In the dimers there are two asymmetrically bridging alkyl groups with one additional terminal alkyl and one phosphine per manganese. The structures show a variation in bond lengths probably due to steric effects, with Mn–Mn distances of 2.667(1)–2.828(1)A, and long Mn–P distances [2.562(1)–2.684(1)A]. There is a close contact between one hydrogen atom on each of the bridging methylene groups and the manganese atom (Mn ⋯ H–C 2.15–2.29 A). Infrared and e.s.r. spectra of the compounds are discussed.

Manganese(IV) alkyl complexes. Synthesis and structure of tetramethyl-[1,2-bis (dimethylphosphino)ethane]manganese(IV)

The interaction of tris(acetylacetonato)manganese(III), Mn(acac)3, with methyl-lithium in the presence of 1,2-bis(dimethylphosphino)ethane (dmpe) in diethyl ether leads, in a disproportionation reaction to Mn Me2(dmpe)2 and to Mn Me 4(dmpe) whose X-ray structure has been determined; also synthesised from Mn (acac)3 are MnMe4(PMe3)2 and the green tetrahedral alkyl complexes MnR4, R = CH2SiMe3 and CH2CMe3 which have been identified spectroscopically.