Kinetic studies are reported of the reaction in ethanol solution between pyridine and several planar platinum(II), palladium(n), and nickel(I1) compounds of the general formula @fClR(PR',),]. The relative rates of attainment of equilibrium of trans-[hlCl(o-tolyl) (PEtJJ with pyridine are approximately 5,000,000 : 100,000 : 1 where M is Ni(zI), Pd(II), and Pt(I1) respectively. The effect on the rates of equilibration of different groups trans to the chloro-group undergoing replacement shows that the translabilizing abilities of these ligands decrease as follows : PMe, > PEt, =:Both the electrostatic (polarization) and x-bonding theories of the trans-effect are needed to explain these results. Mesityl compounds always react more slowly than do analogous aryl derivatives. These observations are discussed in terms of probable mechanisms of planar substitution. Experimental details are also given for the synthesis of new compounds whose dipole moments are recorded. SUBSTITUTION (replacement) reactions of square-planar metal complexes have been studied kinetically, especially those of coinpounds of platinum(I1) which react at rates suitable to be followed by ordinary techniques., The results of these investigations indicate that solvent and/or reactant are involved in the rate-determining step. For reversible reactions of the type reported in this paper: [MCIR(PR'&] + py =s+k [M(R)py(PR'J,]-+ CI-. . . . . . . (1) (where R = alkyl, aryl, o r hydrogen; R' = alkyl) the general rate law for the attainment of equilibrium can be expressed by the equation kobs = k, + k2[py] . . . . . . . . . . * (2)where kobs. is a pseudo-first-order rate constant, k, is a first-order rate constant for solventcontrolled reaction, and k, is a second-order rate constant for reaction with pyridine., This paper reports k, and k, values for a number of such reactions in ethyl alcohol solutions.Neither k, nor k, is a simple rate constant since, for a reversible process, both forward and reverse reactions contribute to the attainment of equilibrium. It may then be expected that a part of k, and also of k , should depend on the chloride-ion concentration, which is certainly involved in the reverse reaction and increases markedly during the course of a kinetic study. Experimentally the effect of changing chloride concentration cannot be detected since a first-order course is followed throughout. This was also observed by Lamb3 in his study of the reversible aquation of [Rh(NH3)5Br]2+, and his explanation may be applicable here, namely, that changes in activity coefficients due to ionic-strength effects roughly cancel changes in concentration. Despite the complex nature of k, and k,, they seem suitable for assessing the relative activating influence of substituents in a series of analogous compounds undergoing the same reaction, since they are independent of concentration over the ranges studied.The results obtained permit (1) a comparison of rates of reaction of analogous nickel(II), palladium(n), and platinum(r1) compounds; (2) an estimate of the tra...

New complexes of the types [RuX,(CO)L,], [RuXY(CO)L,]. [RuX,(CO),L,], and [Ru,X,L6] [anion] (X = C1. Br, or I ; Y = H. CI. Br, I. NO, , acetate, propionate, or benzoate ; L = PR, or AsR,) are described. The hydrido-complexes [RuHX(CO)(PR,),]. configuration (111). react with nitric acid or carboxylic acids to give complexes of the type [RuXY(CO)(PR,),](Y = NO, or carboxylate) but with halogen acids (HY) mixtures are formed. An arsine hydrido-complex [RuHCI(CO) (AsMe,Ph),] is described. The ruthenium-chlorine stretching frequencies for these complexes are recorded and discussed. Tertiary phosphines cause much weakening of a rutheniumchlorine bond in trans-position, and carbon monoxide is a poorly trans-bond weakening ligand but causes more weakening than chlorine as trans-ligand. These bond-weakening effects are discussed. There is good correlation between a low ruthenium-chlorine stretching frequency and a high lability of the chlorine towards nucleophilic displacement; inert chlorines show high ruthenium-chlorine stretching frequencies. The stepwise formation of [RuICI(CO)(PMe,Ph),]and [Rul,(CO)(PMe,Ph),] from [RuCI,(CO)(PMe,Ph),], configuration (11) by nucleophilic displacement of chloride by iodide, has been followed by an n.m.r. method. N.m.r. data and values for vczo are given.A LARGE range of stable carbonyl, dicarbonyl, and hydridocarbonyl complexes of ruthenium(I1) containing neutral ligands (L) such as tertiary phosphines, and halogeno-ligands (X) can be prepared.l* We first describe some new complexes of these types and then show how they and those described previously illustrate trans-bond weakening and trans-bond labilising effects in ruthenium(I1) complexes. The carbonyl complexes described have the configurations (1)-(VI) and the same numbering system as before will be used.The salts of type [Ru2X2L6] [anion] were prepared as described previously; 2p6 several of the complexes are new. Treatment of ruthenium trichloride with PPr2Ph in ethyl methyl ketone gave the ruthenium(1n) complex [RuC13(PPr2Ph),]. Complexes of the type me+ [RuCl,(MEt,Ph),] (M = P or As) have been described previously.MonocarbonyZ ComfiZexes.-These were prepared by established methods, sometimes slightly modified, e.g., when the salt [RU&13(PPr2Ph)6]C1 was treated with

SzcrnmaryThe previous formulation [Pt,(N,H,),(MeNC),]-C1, for Chugaev's salt is shown to be wrong and a structure involving a chelating carbene ligand is suggested.

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LS2 9JT Some new di-t-butylphosphine complexes of the types RuCI,(CO),Q, (two isomers), trans-MX(CO)Q,, MC1,-(CO)Q2, and M' X,Q2 (Q = PHBut2, X = halogen, M = Rh or Ir, M' = Ni, Pd, or Pt) are described. Several n.m.r. parameters including accurate values of 2J(P-M-P) have been calculated from the l H n.m.r. spectra of these complexes. The lH (t-butyl) resonance consists of a five-line pattern of relative intensities 2 : 1 : 2 : 1 : 2 when the two di-t-butylphosphines are mutually trans. Near-and far-i.r. data are given. THERE is considerable interest in nuclear spin-spin coupling constants between phosphorus atoms coordinated to a metal. Approximately 60 such phosphorus-phosphorus coupling constants have been f No reprints available.