Preparation and reactivity of half-sandwich organic azide complexes of osmium

Abstract

Organic azide complexes [Os(η5-C5H5)(κ1-N3R)(PPh3){P(OR1)3}]BPh4 (1, 2) [R = CH2C6H5 (a), CH2C6H4-4-CH3 (b), CH(CH3)C6H5 (c), C6H5 (d); R1 = Me (1), Et (2)] were prepared by allowing bromo-compounds [OsBr(η5-C5H5)(PPh3){P(OR1)3}] to react first with AgOTf and then with an excess of azide in toluene. Benzylazide complexes reacted in solution leading to imine derivatives [Os(η5-C5H5){κ1-NH[double bond, length as m-dash]C(R2)Ar}(PPh3){P(OR1)3}]BPh4 (3, 4) [R2 = H (a, b), CH3 (c); Ar = C6H5, C6H4-4-CH3; R1 = Me (3), Et (4)]. Phenylazide, on the other hand, reacted in solution affording the dinuclear dinitrogen complex [{Os(η5-C5H5)(PPh3)[P(OMe)3]}2(μ-N2)](BPh4)2 (5). Depending on the nature of the R substituent, the reaction of the p-cymene complex [OsCl2(η6-p-cymene)(PPh3){P(OEt)3}] with RN3 yielded imine [OsCl(η6-p-cymene){κ1-NH[double bond, length as m-dash]C(H)Ar}{P(OEt)3}]BPh4 (6) (Ar = C6H4-4-CH3) and amine derivatives [OsCl(η6-p-cymene)(κ1-NH2C6H5){P(OEt)3}]BPh4 (7). The complexes were characterised spectroscopically (IR, 1H, 31P, 15N NMR) and by the X-ray crystal structure determination of [{Os(η5-C5H5)(PPh3)[P(OMe)3]}2(μ-N2)](BPh4)2 (5).

Activation of Dinitrogen by Polynuclear Metal Complexes

“…Of these examples of Cp-(or Cp*) bearing dimetallic N 2 complexes, the osmium compounds were accessed by methods beyond the scope of this review and will not be discussed. 203,204 The first crystallographically characterized Fe−N 2 complex bearing a Cp* ligand was reported in 2008 by Tatsumi and coworkers, 104 (Figure 84). 205 The experimentally determined N−N bond length of 1.132 Å and ν N−N stretching frequency of 2126 cm −1 are comparable to that of many of the reported mononuclear Fe II −(η 1 :N 2 ) compounds supported by phosphine or related strong-field ligands (vide infra).…”

“…Few complexes of the Group 8 metals bearing arene or cyclopentadienyl moieties have been reported compared to other ancillary ligands. Of these examples of Cp- (or Cp*) bearing dimetallic N 2 complexes, the osmium compounds were accessed by methods beyond the scope of this review and will not be discussed. , …”