Synthetic pathways in binuclear molybdenum chemistry: µ-acetato-, chloro-, and tertiary phosphine derivatives; X-ray structure determination of trans-[{MoCl(PBuⁿ₃)(µ-O₂CMe)}₂]

Abstract

The reaction between [(Mo(p-OCOMe),},] and SiMe3CI in the presence of a variety of donor ligands L [tetrahydrofuran (thf), Me2S, Et,S, PEt,, PPh3, PBun3, or Ph2P(CH2),PPh2, where n = 1 or 21 yields binuclear compounds such as [{ M o L C I ( ~-O C O M ~) } ~] or [( MoL2CI,),]. The products may vary according to the stoicheiometry of the reaction. The new compounds described are [{ MoCI(p-OCOMe) (thf)}2], [(MoCI( PPh3) (JJ-OCOM~))~], isomers of [{ MoCl( PEt,) (p-OCOMe)}2], trans-[{MoCI( PBu",) (p-OCOMe)},], and [M0~Cl,(OCOMe)~(dppm)1. Interconversion of some of these compounds by ligand-replacement reactions is also demonstrated. The crystal structure of trans-[{ MoCI( PBu",) (p-OCOMe)},] is described ; the crystals are monoclinic, space group P2, /n, with a = 14.969(2), b = 15.146(2), c = 8.920(2) A, p = 105.14(1)", and Z = 2. Refinement converged with R = 0.048, R' = 0.063, for 1 762 observed reflections [I > 30(1)]. The M o -M o separation is 2.099(1) A. The presence of isomers of the various compounds is demonstrated from the hydrogen-1 n.m.r. spectra. The dimer [{Mo(p-OCOMe),},] (1) has been shown to act as a precursor for the formation of molybdenocene dimers via reaction with sodium cyclopentadienide.' During a study of this reaction we added triphenylphosphine to a mixture of (1) and Na(C5H5) to try to trap out intermediates in the reaction. This work led to the isolation of a new black molybdenocene dimer.2 In order further to understand the role of the PPh3 in the formation of this dimer we wished to synthesise the compounds [{ MoCl(PPh3)(p-OCOMe)),1 and [ { M O C I ~( P P ~~) ~} ~' J . We noticed a report by McCarley et aL3 of the synthesis of [Mo4CI,(PEt3),] from the reaction between [{ Mo(p-OCO-Me)*}?] and chlorotrimethylsilane in the presence of triethylphosphine. This led us to investigate the synthesis of related binuclear compounds using the same general principles.We have found that SiMe3C1 can act as a mild and selective reagent for the replacement of the acetato-groups in (1) by chlorine and thereby can provide a simple and very convenient route to the synthesis of a variety of new and known dimolybdenum compounds, as described below. 7 rrans-Di-~-acetato-OO'-bis[chloro(tri-n-butylphosphine)molybdenum(ri)](4Mo-M0).

Tertiary phosphine ligand-exchange reactions involving the M>M quadruply bonded complexes M2Cl4L4, where L = PMe3, PEt3, PBun3 or PMe2Ph

“…The dimolybdenum compounds Mo 2 Cl 4 (PMe 2 Ph) 4 , Mo 2 Cl 4 (PEt 3 ) 4 and Mo 2 Cl 4 (PMe 3 ) 4 were prepared from Mo 2 (O 2 CMe) 4 by the general procedure described. 21 The ditungsten complexes W 2 Cl 4 (PEt 3 ) 4 , W 2 Cl 4 (PBu 3 ) 4 and W 2 Cl 4 (PMe 3 ) 4 were prepared from the reduction of WCl 4 by the general procedure described. 22 The phosphine ligands PMe 3 , PEt 3 , PBu n 3 , PMe 2 Ph and PMePh 2 were purchased from Aldrich and the diphosphine ligand dmpe from Strem.…”

Further attempts to rationalise the co-ordination chemistry of manganese with Schiff base ligands and supplementary carboxylate donors

“…First, we wished to discover whether it was a straightforward procedure to replace the acetylacetonate ligand, and, secondly, to see whether such a reaction could lead to the formation of cluster compounds. This reagent has previously been employed as an abstractor of carboxylate ligands co-ordinated to metal centres 16 and has subsequently been employed in this manner to prepare manganese clusters. 17 The reaction of [Mn(salpn)(acac)] with Me 3 SiCl in dry degassed acetonitrile resulted in the formation of a compound of stoichiometry Mn(salpn)Cl in 61% yield (see Table 2).…”

“…21 Our attempts to isolate manganese() complexes with ancillary carboxylate ligands, as indicated, have been largely unsuccessful, manganese() complexes of stoichiometry Mn(L)ؒnH 2 O being isolated routinely. However, on one occasion, in the reaction of 5NO 2 -salpn with manganese() acetate tetrahydrate, we have been able to isolate a manganese() species from the reaction liquor after removal of the precipitated manganese() complex and slow evapor- 7) 92.17 (17), O(2)-Mn(1)-O(7) 89.94 (17), N(2)-Mn(1)-O(7) 81.68(18), N(1)-Mn(1)-O(7) 84.69 (19), O(8)-Mn(1)-O(7) 173.26 (16). monomers, Mn-O(8) 2.123(4) Å, whilst the manganese-water distance is intermediate between 1 and 4 at 2.347(5) Å.…”

N-Heterocyclic Carbene Adducts of Molybdenum Tetracarboxylate Complexes

“…During the course of our studies, attempts were made to further functionalize the [Mo 2 ] core by reaction of the NHC adduct systems, specifically complex 2d , with trimethylsilyl chloride (TMSCl) in effort to generate NHC analogues of the phosphine adduct [Mo 2 Cl 4 (PR 3 ) 4 ] (R = Me, Et, Me 2 Ph) and [Mo 2 (μ-OAc) 2 Cl 2 (PR 3 ) 2 ] (R = Bu, Ph). − Reaction of 2d with an excess of TMSCl resulted in an immediate color change from red to dark purple (Scheme ), and cooling of the reaction mixture to −28 °C resulted in the formation of a crop of red crystals.…”