The concerned azooximes (L1OH, 1) are of type p-X-C6H4C(N2Ph)(NOH) (X = H, Me, Cl). The reaction of [Re(MeCN)Cl3(PPh3)2] with [Ag(L1OH)(L1O)] in cold dichloromethane-acetonitrile solvent has furnished the green colored ionized azoimine complex [ReV(O)Cl(PPh3)2(L1)](PF6), 2. In effect L1O- has undergone oxidative addition, the oxygen atom being transferred to the metal site. Upon treatment of [ReV(NPh)Cl3(PPh3)2] with L1OH in solution, the neutral azoimine complex [ReV(NPh)Cl3(L1H)], 3, resulted due to the spontaneous transfer of the oxime oxygen atom to a PPh3 ligand, which is eliminated as OPPh3. In contrast, the oxime of 2-acetylpyridine (L2OH, 4) did not undergo oxygen atom transfer and simply afforded the imine-oxime complex [ReV(NC6H4Y)Cl2(PPh3)(L2O)], 5, upon reacting with [ReV(NC6H4Y)Cl3(PPh3)2] (Y = H, Me, Cl). The spectral and electrochemical properties of 2, 3, and 5 and the structures of three representative compounds are reported. In the cation of 2 (X = H) the two PPh3 ligands lie trans to each other and the equatorial plane is defined by the five-membered azoimine chelate ring and the oxo and chloro ligands. The oxo ligand which forms a model triple bond (Re-O length 1.616(6) A) lies cis to the imine-N atom. In 3 (X = Cl) the ReCl3 fragment has meridional geometry and the imido nitrogen lies trans to the imine nitrogen of the planar azoimine chelate ring. In 5 x H2O (Y = Me), the Cl, oximato-N, and P atoms define an equatorial plane and the pyridine-N lies trans to the imido-N. The water of crystallization is hydrogen bonded to the oximato oxygen atom (O...O, 2.829(5) A). Reaction models in which chelation of the azooxime precedes oxygen atom transfer are proposed on the basis of oxophilicity of trivalent rhenium, Lewis acid activity of pentavalent rhenium, electron withdrawal by the azo group, and observed relative disposition of ligands in products.

Organometallics of type [Ru(C 6 H 2 O-2-CHNHC 6 H 4 R-3-Me-5)(PPh 3 ) 2 (CO)(Cl)], 3 (R ) H, Me, OMe, Cl), incorporating a four-membered C,O chelate ring smoothly react with CNBu t in benzene solution affording the yellow-colored organoruthenium imidic ester hydrochloride system [Ru(C 6 H 2 OCN(Bu t )HCl-2-CHNC 6 H 4 R-3-Me-5)(PPh 3 ) 2 (CO)(CNBu t )], 4, in which a fivemembered C,C chelate ring is present. While stable in the solid state, 4 is spontaneously reactive in solution, furnishing the red-colored chelate [Ru(C 6 H 2 (CO-1)O-2-CHNHC 6 H 4 R-3-Me-5)(PPh 3 ) 2 (CNBu t )(Cl)], 5, incorporating five-membered acyl-phenolato C,O chelation. Chloride elimination from 5 by excess CNBu t furnishes [Ru(C 6 H 2Characteristic spectral features of the families are reported. A notable electrochemical feature is that the Ru(III)/Ru(II) reduction potential increases with increasing number of carbon atoms in the coordination sphere: 5 < 6 + < 4. The X-ray structures of 4(Me), 5(H), and [6(Me)]Cl‚2CH 2 Cl 2 are reported. The equatorial coordination planes are RuC 4 , RuC 2 OCl, and RuC 3 O, respectively, the axis being uniformly defined by the trans RuP 2 fragment. Both 5(H) and 6(Me) + display iminium-phenolato N-H‚‚‚O hydrogen bonding, while in 4(Me), N-H‚‚‚Cl and C-H‚‚‚O hydrogen bondings are present. In the transformation 3 f 4, one CNBu t molecule displaces the chloride ligand and another inserts into the Ru-O bond, generating a chelated imidic ester function. In 4(Me) the Ru-CO bond (1.891(8) Å) lying trans to the imidic ester carbon is ∼0.1 Å longer than that in the precursor complex 3(Me). The Ru-C(aryl) distance is also longer in 4(Me) by 0.04 Å. Thus both the bonds are activated by isonitrile insertion and the transformation 4 f 5 occurs spontaneously with C-C bond formation via aryl migration attended with isonitrile elimination, the reaction following first-order kinetics. The activation parameters determined for the 4(Cl) f 5(Cl) reaction are ∆H q , 18.72(1.00) kcal mol -1 , and ∆S q , -17.89(3.20) eu, implying that the transition state is ordered but with an excess of net bond breaking over net bond formation. Logarithmic rate constants are found to vary linearly with the Hammett constant of the R substituent, consistent with nucleophilic aryl migration.

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The title complexes of type M(RL2)(PPh3)2(CO)(S2CSEt) (2a: M = Ru; 2b: M = Os) have been synthesized in excellent yields by reacting M(RL1)(PPh3)2(CO)X (1a: M = Ru, × = Cl; 1b: M = Os, × = Br) with potassium ethyl thioxanthate and have been characterized with the help of spectral and electrochemical data. The RL2 ligand in 2 is the imine‐phenol tautomer of N‐C6H4R(p)‐4‐methylsalicylaldimine (R = Me, MeO, Cl) coordinated at the carbanionic‐C2 atom only while RL1 in 1 is the iminium‐phenolato tautomer chelated via carbanionic‐C2 and phenolato‐O atoms. The synthetic reaction is thus attended with tautomerization of the Schiff base ligand. It is also associated with a rotation of the ligand by ˜180° around the M–C bond in order to exclude steric repulsion. These features have been revealed by structure determination of 2a (R = Me). The metallated aldimine ring is found to be highly noncoplanar (dihedral angle ˜40°) with the thioxanthate chelate ring due to steric repulsion originating from the relatively large size of the sulfur atom. This phenomenon, which is absent in both the precursor 1 (R = Me) and in the carboxylate analogue Ru(MeL2)(PPh3)2(CO)(O2CMe), 7, has distinctive effects on bond parameters of 2a (R = Me). Thus the two Ru–P bonds in 2a (R = Me) differ in length by as much as 0.06 Å. The thioxanthate 2 is thermodynamically more stable than the precursor 1 as well as the carboxylate 7. Accordingly, both of these are irreversibly transformed to 2a (R = Me) upon treatment with thioxanthate.

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