The osmium(VI) nitrido complex TpOs(N)Cl(2) (1) has been prepared from K[Os(N)O(3)] and KTp in aqueous ethanolic HCl. It reacts rapidly with PhMgCl and related reagents with transfer of a phenyl group to the nitrido ligand. This forms Os(IV) metalla-analido complexes, which are readily protonated to give the analido complex TpOs(NHPh)Cl(2) (4). The nitrido-phenyl derivatives TpOs(N)PhCl and TpOs(N)Ph(2) react more slowly with PhMgCl and are not competent intermediates for the reaction of 1 with PhMgCl. Reactions of 1 with alkyl- and arylboranes similarly result in transfer of one organic group to nitrogen, leading to isolable borylamido complexes such as TpOs[N(Ph)(BPh(2))]Cl(2) (11). This is an unprecedented insertion of a nitrido ligand into a boron--carbon bond. Hydrolysis of 11 gives 4. Mechanistic studies suggest that both the Grignard and borane reactions proceed by initial weak coordination of Mg or B to the nitrido ligand, followed by migration of the carbanion to nitrogen. The hydrocarbyl group does not go to osmium and then move to nitrogen--there is no change in the atoms bound to the osmium during the reactions. It is suggested that there may be a general preference for nucleophiles to add directly to the metal--ligand multiple bond rather than binding to the metal first and migrating. Ab initio calculations show that the unusual reactivity of 1 results from its accessible LUMO and LUMO + 1, which are the Os = N pi* orbitals. The bonding in 1 and its reactivity with organoboranes are reminiscent of CO.

When arylboranes react with the osmium(VI) nitrido complex [{HB(pz)3}Os(N)Cl2], they do not just bind to the nitrogen atom. A B−C bond is cleaved, and the phenyl and boryl units are separately bound to nitrogen in the product (e.g. 1; X=Ph; Y=Ph, OBPh2). Subsequent hydrolysis leads to cleavage of the B−N bond and generation of the anilido species [{HB(pz)3}Os(NHPh)Cl2]. pz=pyrazolyl.

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NO is a common and important ligand in transition metal chemistry, from biological systems to organometallic compounds to industrial catalysts. 1 Complexes of the analogous sulfurcontaining ligand, thionitrosyl, are less common and were not known until 1974. 2 Despite synthetic efforts, related complexes containing the heavier chalcogens, selenium and tellurium, have not yet been reported in the literature. 3 This contrasts with chalcocarbonyl ligands, for which the first complete series was described in 1980. 4 In this report, we detail the synthesis and properties of a homologous series of chalconitrosyls, TpOs(NE)-Cl 2 (E ) O (2), S (3), Se (4); Tp ) hydrotris(1-pyrazolyl)borate), including the first example of a transition metal selenonitrosyl complex. Compounds 2-4 were synthesized by atom transfer to the terminal nitrido complex TpOs(N)Cl 2 (1).The syntheses of compounds 2-4 are outlined in Scheme 1. 5 The light purple nitrosyl complex, TpOs(NO)Cl 2 (2), is formed in 20% yield by treatment of 1 with excess trimethylamine-Noxide in methylene chloride at 80 °C for 2 days. The only other example of an oxygen atom transfer to a nitrido complex to give a nitrosyl is the formation of [Os(tpy)(NO)Cl 2 ][BF 4 ] from Me 3 -NO and [Os(tpy)(N)Cl 2 ][BF 4 ] (tpy ) 2,2′:6′,2′′-terpyridine). 6 In both cases the nitrido seems to be acting as an electrophile as no reaction is observed with use of the less nucleophilic pyridine-N-oxide. The forest green thionitrosyl complex, TpOs(NS)Cl 2 (3), is prepared in 77% yield by sulfur atom transfer from propylene sulfide at ambient temperatures. S 8 can also serve as the sulfur atom source, but reaction with 1 requires heating and proceeds only in moderate yield. Such sulfur atom transfer to metal nitrido complexes is a common route to thionitrosyl complexes. 7 The selenonitrosyl complex, TpOs(NSe)Cl 2 (4), is slowly formed by heating 1 in the presence of excess selenium metal (gray) in methylene chloride. After 5 days at 80 °C, a 28% yield of forest green 4 is isolated after chromatography on silica gel, in addition to ∼50% unreacted 1. Attempts to extend this

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