6983
sence of Cl-); (2) that cis-Co(tetb)CIOHzz+ cannot be seems very much out of order. Despite the detected as a transient in reaction 1 and has not been presence of the azomethine groups the trans[ 14ldiene prepared by other methods; (3) that Co-C1 bonds are ligand seems quite flexible; certainly the steric differgenerally about aslabile as Co-OH, bonds;29and(4) that ences between the macrocyclic ligands are too small to trans-Co(tetb)(OHz)Z3+ does not seem to be an imporbe obvious from examination of molecular models of cis-Co(trans[ 14]diene)(OHz)z3+ and cis-Co(tetb)(OHz)z3+. tant product of reaction 1. These considerations suggest that reaction 1 may proceed by means of a nucleoA more likely hypothesis is that the presence of Co-Nphilic attack of C1- at the organic backside of cis-Co(imine) bonds in the trans[ 14ldiene complex stabilizes (tetb)( OH,), 3+. a CoLOHz3+intermediate. The kinetic stability of ~is-Co(tetb)(OH~),~+ is to be Acknowledgments. The authors wish to express contrasted with the rapidity of reaction 1. A further their gratitude to Professor R. B. Jordan for making and even more remarkable contrast is that C1- inhibits some of his work available to them prior to publication. the cis + trans isomerization of Co(~yclam)(OH~)~~+.* They also wish to acknowledge their stimulating and critical discussions with Dr. Noel A. P. Kane-Maguire. It should also be noted (1) that Co-0 bond breaking should lead to cis + trans isomerization (even in the ab(29) Reference 23, Chapter 3.
Chlorotris ( triphenylphosphine) iridium (I ) and Related Complexes. Oxidative Addition Reactions and Hydrogen Abstraction from the Coordinated Ligand' M . A. Bennett2 and D. L. Milner Contribution from the William Ramsay and Ralph Forster Laboratories, University College, London, and the Research School of Chemistry, Australian National University, Canberra, A.C.T., Australia. Received June 24, 1969 Abstract: The preparation, properties, and reactions of a series of complexes of general formula IrCIL3 are described, where L is (C6H&P,(C6D&P, (o-DCGH&P,( P - F C ~ H ~(P-CH?OC6H&P, ~P, (p-CH3C6H&P,(C6H&As, and (C6H5)&. The complex IrC1(Ph3P)3differs from the analogous rhodium compound in two principal ways : (i) triphenylphosphine is not so readily lost in solution; (ii) the reaction with hydrogen is irreversible and occurs without displacement of triphenylphosphine, so that IrC1(Ph3Ph does not function as a homogeneous hydrogenation catalyst. Reactions with CO, PF3, NO, and HCl are described. Reaction of IrCl(Ph3P)8with chlorine gives initially an iridium(II1) complex IrC13(Ph3P)2,which appears to be five-coordinate in solution, and with excess chlorine or nitrosyl chloride the iridium(1V) complex IrCl,(Ph3P)2 is formed. This and the analogous triphenylarsine complex are characterized by far-infrared, magnetic susceptibility, and esr measurements. Metal-chlorine stretching frequencies are reported for the new compounds and used where possible to assign stereochemistries. Unlike their rhodium analogs, the iridium(1) complexes IrC1L3isomerize on heating in solvents to octahedral hydrido aryls of iridium(III), the stereochemistry of which is inferred from infrared and proton nmr measurements, It is shown that the isomerization arises by transfer of one hydrogen atom from the ortho position of an aromatic ring of the coordinated ligand to the metal, with the formation of a metal-carbon c bond at the ortho position. In the triarylphosphine series, the rate of isomerization depends on the substituent para to phosphorus in the order F < H < OCH3 < CHI. On the basis of the small kinetic isotope effect, a three-center mechanism is suggested for the hydrogen transfer. The reactions of the hydrides are generally similar to but slower than those of the parent iridium(1) complexes. Some of these reactions apparently proceed uiu the iridium(1) complex formed by return of the hydrogen to the ligand. The iridium(1)-iridium(II1) tautomerism is compared with similar situations involving Fe(0)-Fe(I1) and Ru(0)-Ru(II), and a brief analogy is drawn with metal-catalyzed H-D exchanges in aromatic hydrocarbons.
T
he ability to undergo oxidative addition reactions with a variety of simple molecules and to catalyze the homogeneous hydrogenation of olefins and acetylenes are features of a number of d8 metal complexes, notably IrC1(CO)(Ph3P)23and RhCl(Ph3P)3. 4 , 5 On the (1) Preliminary communication: M. A. Bennett and D. L. Milner, Chem. Commun., 581 (1967); presented in part at the Symposium on Transition Metal Complexes of Hydrogen, Oxygen, and Nitrogen and Homogeneous Catalysis, Osaka, Japan, Sept 22, 1967. (2) Author to whom enquiries should be addressed at the Research School of Chemistry, Australian National University, Canberra, Australia.
basis of the limited data presently available, it appears that (a) iridium(1) complexes undergo oxidative addition more readily than rhodium(1) complexes, and (b) oxidative addition is assisted by the presence of good a-donor ligands on the metal. We therefore decided to attempt the preparation of IrCl(Ph3P)3, expecting (3) L. Vaska and J. W. D i Luzio, J . Amer. Chem. SOC.,83,2784 (1961). (4) M. A. Bennett and P. A. Longstaff, Chem. Ind. (London), 846 (1965). (5) J. A. Osborn, F. H. Jardine, J. F. Young, and G. Wilkinson, J . Chem. SOC.,A , 1711 (1966).
Bennett, Milner
/ Chlorotris(triphenylphosphine)iridium(l)
6984 Table I. Analytical Data and Ir-C1 Stretching Frequencies in Complexes of General Formula IrClLp
---zc--
Formula of complex
Color
IrCI{(CsHdaP}3 IrBr {(CsH&P\3 IrC1 {(CsD&P}3 IrCl((o-DC6Ha)3P)a IrCl((p-FC6Ha)pP]3
Orange Red-brown Orange Orange Orange
63.7 61.8 61.2 63.4
IrCl((p-CH30CsH4)3P)3Orange IrCl{(p-CH3C6H4)3P}3Orange IrCl{(CsH&AS)3 Orange-red IrCl ((CsH;),Sb! 3 Red
58.9 66.7 56.6 50.4
x
---x
%H-CI/BrPv(1r-Cl), CalcdFound Calcd Found Calcd Found Calcd Found cm-1 63.7 62.0 59.5 62.7 5 5 . 0 55.2
4.8 4.3
4.7 4.3 5.5* 3.0
3.5 7.6 3.3 3.5 3.0
3.4 7.4 3.4 3.5 3.1
3.5 3.1
56.1 67.2 55.6 51.4
5.0 5.6 4.0 3.5
4.9 5.7 4.4 3.9
2.8 3.1 3.1 2.8
2.7 3.0 3.2 2.6
9.1
9.26
8.8
8.2
7.9
7.8
282s
420s, 321 w, 243 w, 223 m 414 s, 320 w, 220 w nm nm nm nm 283s 43Os,35Ow,34Ow,24Ow, 233 w 284 ms 445 vs, 438 vs 279 s 440 vs, 420 ms, 353 m nm nm nm nm
a Abbre viations: s, strong; vs, very strong; m, medium; ms, medium strong; w, weak; nm, not measured. calcd 1015; found (CsHa) 800-850, (CHCL) 700-750.
that it would be more reactive than either IrCl(C0)(Ph3P)2or RhC1(Ph3P), and hoping that it would be an even better homogeneous hydrogenation catalyst. The reaction of the metal chloride in ethanol with excess triphenylphosphine, which provides an easy preparation of RhC1(Ph3P)3,4~5 cannot be used to make IrC1(Ph3P)3,since the initially formed hydrido complex IrHClz(Ph3P)3,6unlike its rhodium analog,' does not readily eliminate HC1; this can only be achieved with a reagent such as (CH3)3SnN(CH3)2.8During the course of our work, the presence of IrCl(Ph3P)3 in the solution obtained by treating the nitrogen complex IrC1N2(Ph3P).? with triphenylphosphine was sugge~ted,~ and later the desired complex was isolated. lo Following our initial communication,1 we now report the preparation and properties of a series of complexes of general formula IrCl(ligar~d)~ and details of their isomerization to hydrido complexes of iridium(II1). Results We' first isolated I I - C I ( P ~ ~ Pby) ~heating the 1,5cyclooctadiene complex [IrCl(C8H12)]211with excess triphenylphosphine in ligroin; a similar method has been used to make RhC1(Ph3P)3.12 In the first stage of the reaction, which occurs at room temperature, the halogen bridges of the diene complex are split, giving IrC1(CsH1?)(Ph3P); on heating, the diene is displaced and IrCl(Ph3P)3 precipitates as orange crystals. Since [ I T B T ( C ~ His~ ~unstable, )]~ an indirect method has to be used to make 1rBr(Ph3P),. On heating with lithium bromide, IrC1(CsH12)(Ph3P) is converted to the corresponding bromo complex, and this, when heated with excess triphenylphosphine in ligroin, gives orange crystalline IrBr(Ph3P)3. Using triphenylarsine and triphenylstibine, the analogous diene complexes IrCl(CaHI2)(Ph3M) (M = As, Sb) can be obtained,I3but the diene cannot be replaced, presumably owing to the poorer u donor ability of these ligands compared with triphenylphosphine. The most convenient starting point for making the complexes IrClL3 (L = triarylphosphines, PhaAs, and (6) L. Vaska, J . Amer. Chem. Soc., 83, 756 (1961). (7) A . Sacco, R. Ugo, and A. Moles, J . Chem. Soc., A , 1670 (1966). ( 8 ) D. J. Cardin and M.F. Lappert, Chem. Commun., 1034 (1967). (9) J. P. Collman and J. W. Kang, J . Amer. Chem. Soc., 88, 3459 (1 966). (10) J. P. Collman, M. Kubota, F. D. Vastine, J. Y . Sun, and J . W. Kang, ibid., 90, 5430 (1968). (11) G. Winkhaus and H. Singer, Chem. Ber., 99, 3610 (1966). (12) I
