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The reaction of co-ordinate8 dinitrogen in a well defined manner to form organonitrogen ligands was first noted in the reaction of organic acid halides with [M(N,),( dppe),][dppe = 1 ,Z-bis( diphenylphosphino)ethane] and [ReCl(N,)(PMe,Ph),L] to form acyl-and aroyl-diazenido-complexes.3 Since then there have been brief reports of the reactions of the molybdenum and tungsten bis(dinitrogen) complexes with alkyl halides under irradiation to give alkyldiazenido-and related complexes,4*5.11,12 and with tetrahydrofuran (thf) to form complexes which were tentatively described as tetrahydropyridazido-complexes 1, but were recently shown to be w-diazobutanol c0mp1exes.l~ Here we describe in detail the work briefly reported in refs. 3 and 4. RESULTSAcyldiazenido-and Aroyldiazenido-complexes and their Derivatives --,4cyl and aroyl halides react with the com-(PR3)J (py = pyridine) to form acyldiazenido-and aroyldiazenido-complexes.3 The products containing molybdenum or tungsten are most easily isolated as the hydrochlorides, formulated [MC1,(N2HCOR) (dppe),] (R = alkyl or aryl). One mol of hydrogen chloride can be removed by plexes [M(N,) z(dPP4 21. tReCI(N2) (PR3)4J 2 or [ReCW,) (PYb pqx,).(dppe),] -t-RCOC~ -1-HCI + [NICl,(N,HCOR) (dppe) ?] NEt, HCI [i?ICl( N,COII) (clppe) ,] ( 1)bases, as shown in (1). Acylation and aroylation of the rhenium dinitrogen complexes analogously yield [ReCl,-(N,COR) (PRJJ, b u t the resulting diazenido-ligand is not protonated by hydrogen chloride. These complexes (with R = aryl) have been obtained previously from aroylhvdrazines,15 but the acyldiazenido-complex is the first of its type. The complexes [OsCl,(N,) (PR3)3], which are isoelectronic in the valence shell with the rhenium, molybdenum, and tungsten complexes, do not react with acyl or aroyl halides, even in toluene under reflux.

Electron Spin Resonance Spectra of Trigonal-prismatic Bis[pentane-2,4dione benzoylhydrazonato(2--)]vanadium(iv) and Bis[4-phenylbutane-2,4-dione benzoylhydrazonato(2-)]vanadium( IV)

The reaction between pyridoxamine and pyruvic acid in water a t 25" over the range pH 7-10 yields pyridoxal and alanine. Kinetic and spectroscopic studies show that the reaction proceeds by the fast and reversible formation of the Schiff's base. The rate-limiting step, which is general-acid catalysed, is the interconversion of this and the isomeric Schiff's base, i.e., the change *CH=N.CHMeCO,H *CH,*N=CMe*CO,H. The reverse reaction (formation of pyridoxamine and pyruvic acid) has also been studied, but in less detail. SNELL and his co-workers1 have shown that many of the enzymic reactions in which pyridoxal 5'-phosphate is involved as co-factor can be simulated in vitro by heating a mixture of an appropriate amino-acid, pyridoxal, and a metal-ion catalyst. Following earlier suggestions suggested that the transamination proceeds essentially as shown in scheme (A) (which for simplicity has been written without reference to ionic states or to the formation of chelates between the intermediates and any metal ions present in solution).The mechanism of the reactions is discussed. that imine intermediates are involved, Snell and his co-workers Intermediates of type (I) and their metal chelates (C,) have been i~o l a t e d .~ Semiquantitative kinetic studies 5 support the view that under Snell's conditions reaction proceeds via metal chelates CI and CLI. Metzler showed that in aqueous solution, imines * Banks, Diamantis, and Vernon:(e.g., I) are rapidly and reversibly formed from pyridoxal and amino-acids, and the equilibrium constants involved were measured spectrophotometrically. Matsuo found that similar reactions occur with pyridoxal5'-phosphate in ethanol and that, under these conditions, transamination occurs readily even in the absence of metal-ion catalysts. EXPERIMENTALMaterials.-Pyridoxamine hydrate crystallised from an aqueous solution of pyridoxamine dihydrochloride which had been neutralised with sodium hydroxide. It was washed with water and methanol and twice recrystallised, under nitrogen, from water (Found: C, 47.4; H, 8.1; H20, 16.6. Calc. for C8H,,N204: C, 47.0; H, 8.4; H20, 17.5%). The dissociation constants pKa,1, PKa,,, P K~,~, determined by titration with a glass electrode, were 3.33, 8-08, and 10.33, respectively.Pyridoxal ethyl acetal hydrochloride (Roche Products Ltd.) was dissolved in water and heated a t 60°, for 10 min.; pyridoxal separated after addition of an equivalent of sodium hydrogen carbonate and was recrystallised, under nitrogen, from water (Found: C, 57-2; H, 5.7. Calc. for C8H,N03: C, 57.5; H, 5.4%).DL-Alanine (B.D.H.), when recrystallised from aqueous ethanol, was chromatographically homogeneous.Commercial samples of N-methyldiethanolamine, NN-dimethylethanolamine, and triethanolamine were distilled under reduced pressure. Values of pK, were 8.61, 9-33, and 8.00 respectively.NN-Dimethylglycine hydrochloride was a commercial sample (Found : equiv., 140.4. Calc. for C4H,,C1N02: equiv., 139.6), pK, 9-70.Potassium pyruvate was obtained by adding freshly distilled pyruvic acid, b. p. ...