Ph,AsCH,CH,AsPh, (dpae) ; cis-Ph,PCH=CHPPh, (dppen) ; cis-Ph,AsCH=CHAsPh, (dpaen) ; Ph,AsCH,-CH,PPh, (dadpn) ; cis-Ph,AsCH=CHPPh, (dadpen) ; and C,H,(AsPh,-o) (PPh,-o) (pdadp)] has led to the isolation of [MoCI,O(L-L)] complexes. Refluxing these complexes in methanol leads to partial reduction to form [MoxVCIO(L-L),][MoVCI,O], but reflux in methanol in the presence of L-L and Na[BPh,] results in complete reduction to [MoCIO(L-L),] [BPha]. These complexes have been characterised by the use of i.r.. electronic-absorption, and e.p.r. spectroscopy. E.p.r. spectra suggest that the [MoCI,O (L-L)] (L-L = dppe or dppen) species have a fac structure in dichloromethane. Considerable hyperfine structure, and g values ca. 1.97, have been observed for the e.p.r.-active species. C6H,(PPh2-o), (pdpp) ; * This complex has previously been prepared from [MoCl,O-(thf),] (thf = tetrahydrofuran) .6

The preparation of oxomolybdenum(v) complexes [MoOCI,( L-L)] with the bidentate ligands (L-L) 1,3-bis(di-methy1phosphino)propane. 1.3-bis(dimethylarsino)propane. (3-dimethylphosphinopropyl)dimethylarsine, ophenylenebis(dimethy1arsine). and (2-dimethy1arsinophenyl)dimethylstibine are described. On the basis of their e.s.r. spectra the first three complexes have fac structures. Oxomolybdenum(1v) cations [MoO(CI) (L-L),] + have been prepared from [MoOCI,(PMe,Ph),] and L-L, and are shown by lH n.rn.r. to have trans-pseudo-octahedral structures. WE recently reported4 the synthesis of a range of oxomolybdenum(v) complexes of phenyl-substituted Oxomob!ybdenum(v) CompZexes.-The reaction of [Mo-' phosphorus and arsenic bidentate ligands, [MoOCl,-OCl,( thf),] (thf = tetrahydrofuran) with o-phenylene-(L-L)] , and their reduction under appropriate conditions bis(dimethy1arsine) (pdma) ,t (2-dimethylarsinopheny1)to oxomolybdenum(1v) cations, [MoO(Cl) (L-L),] +. The dimethylstibine (dmads), 1,3-bis(dimethylphosphino)properties of the complexes and the conditions under propane (dmpp) , 1 ,3-bis(dimethy1arsino) propane (dmap) , RESULTS AND DISCUSSION

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