Nitrito ligand

NO disproportionation has been shown to be promoted by the Mn(II) tropocoronand complex Mn(TC-5,5) (82) (Eq. (38)), and the reaction was found to involve three equivalents of NO leading to formation of N20 and O-coordinated nitrito ligand. The electron balance is provided by oxidation of Mn(II) to Mn(III). The mononitrosyl complex Mn(TC-5,5)(NO) was proposed to react with NO to produce an unstable cis-dini-trosyl, Mn(TC-5,5)(NO)2, which is then poised to form an N-coordinated hyponitrito (0=N-N=0) ligand from which oxygen transfer occurs to another NO (82a). The intermediacy of a hyponitrito ligand parallels other proposed mechanisms for metal complex promoted NO disproportionation (5a-d). 

In this paper author reported the reactivity of newly synthesized Co(III)-nitrosyls complexes with superoxide radical to follow nitric oxide dioxygenation. Two new Co(III)-nitrosyl complexes bearing N-tetramethylated cyclam (TMC) ligands, [(12-TMC)-Com(NO)]2+ (1) and [(13-TMC)Coin(NO)]2+ (2), were synthesized via [(TMC)Con(CH3CN)]2+ + NO(g) reactions. Spectroscopic and structural characterization showed that these compounds bind the nitrosyl moiety in a bent end-on fashion. Complexes 1 and 2 reacted with K02/2.2.2-ciyptand to produce [(12-TMC)Con(N02)]+ (3) and [(13-TMC)Con(N02)]+ (4), respectively these possess 0,0 -chelated nitrito ligands. 

Mechanistic studies using 180-labeled superoxide (1802 ) showed that one O atom in the nitrito ligand is derived from superoxide and the O2 produced comes from the other superoxide O atom. Evidence supporting the formation of a Co-peroxynitrite intermediate is also presented. 

The tight 7t-bonded intermediate is consistent with a negative volume of activation. It also explains the (unanticipated) O-to-O exchange in the nitrito ligand at a rate comparable to the O-to-N isomerization (Sec. 2.2.2). ATj/Atj = 1.2 ... 

Unlike Co—NO complexes (Section 47.4.1.3), the reactivity of coordinated nitro and nitrito ligands toward electrophiles is not well explored. However Tovrog and his colleagues at Allied Chemical Corporation have recently shown that (28) catalytically oxidizes PPhj in a bimolecular transfer of O from coordinated NO2 (equation 23), ° and that (28) and the similar porphyrin complex [Co(TPP)(py)(N02)] both catalyze the oxidation of primary and secondary alcohols to aldehydes and ketones in the presence of the Lewis acids BFj HjO or LiPF non-radical pathways are proposed. Internal redox in [Co(N02)2(bipy)2]X also occurs on heating, with oxygen transfer, to give the Co complex [Co(N03)X(bipy)2] and NO (X = Cl , Br , I , CIO3 , CIO ). ... 

N-coordinated or 0-coordinated modes. To indicate the alternative donor atom through which an ambidentate ligand is coordinated in a particular complex, we may use the kappa convention, indicating the atomic symbol (in italics) of the donor atom by that Greek letter. Thus, we could refer to the nitrito ligand as NO2-KN or NO2-KO (Scheme 1). 

Linkage isomerization of the nitrito ligand to the nitro form [equation (42)] has already been discussed in Section 5.7.6, q.v. 

The kinetics of solvolysis of complexes cis- and // a 5-[Pt(N02)2L2] (L=ammonia, pyridine, or triethylphosphine) in acetic acid-sulphuric acid mixtures have been compared with those in aqueous sulphuric acid. The mechanism is loss of a nitro-sonium ion from the protonated complex. Whether this protonation takes place at the nitrito-ligand or at the metal is not known, but definitive evidence favouring the latter could not be obtained. Platinum-carbon bond cleavage in cw-[Pt(C6H4Y)2-(PEt3)2], studied in methanol and methanol-water mixtures, takes place by electrophilic attack by a proton,... 

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