Chem.Rev. 1981. 81. 79-90
79
Complexes of the Platinum Metals Containing Weak Donor Ligands J. A.
DAVIES' and F. R. HARTLEY'
oapamnsnf of chsnxshyand MetaIbgy. The Roya/ MlWaty Cekge 01 &&me, SMVsnham, Swhwlon. Wh.. Engfnnd Receh& September 3. 1980 (Revlred Manuscrbt Recehd Decsmber 1. 1980)
Contents I. Introduction 11. Metal-Ligand Interactions: An Approach to the Phenomenon of Weak Bonding 111. Complexes of the Platinum Metals Comalnlng Weak Donor Ligands A. Sulfoxide Complexes (Particularly Dlmethyl Sulfoxide) E. Amide Complexes (Parlicularly Dimethylformamide) C. Pyridine Complexes D. Drganonitrile Complexes E. Complexes of OxygenDonor Lmnds 1. Aquo Complexes 2. Alcohol Complexes 3. Ether Complexes 4. Ketone Complexes F. Coordination of Classically "Noncwrdlnating" Anions IV. Preparative Techniques A. OxMation Methods Using Nlbownlum Salts 8. Halide Abstraction Reactions C. Ligand Displacement by Hydrogenation D. Solvolysis of Metal-Halide Bonds E. Photolysis Reactions V. Catalylic Considerations VI. Conclusions VII. Acknowledgments VIII. References
79 79 82 83 83 84 84
85 85 85 86 86 87 87 87 87 87 88 88 88 88 89 89
Frank R. Haftky Is Head of the Department of Chemisby and Metallugy In the Royal Military College of Science at SMvenkam. Oxfordshire. He graduated from Magdalen Calm. Oxford, wlth an M.A. and a D.Phi1. In Chemistry in 1966, and became a Research Scientist wlth C.S.I.R.O.. Division of hoteln Chemistry, Melbourne. Ausbatia. He returned to England to become an IC1 Research Fellow in University College London In 1969. and was Lecturer in Inorganic Chemistry in the Universky of Soulhampton from 1970 to 1975. He is a Fellow of the Royal Society of Chemistry and the a t " of three books, "Chemistry 01 Platinum and Palladium". "The Elements of Organometallic Chemistry".and "Solution Equilibria". His current research interests lie in the a p plication of organometallic and cowdimtion chemistry to the syw thesis of both homogeneous and poiymer-supported cataiysts.
I. Introductbn Many complexes of the platinum metals mu, Os, Rh, Ir, Pd, and Pt) have been shown to act as active homogeneous catalysts in reactions of industrial importance, including the hydrogenation,'Z hydrosilation,3.' hydroformylation,5Eand oxidative hydrolysi~~.~ of olefins and the carbonylation of methanol?,'0 Some success in the activation of alkanes has also been achieved by complexes of these metals." The ease with which an organic substrate can enter the coordination sphere of a metal ion is thought to be a key factor in determining the ability of such an ion to catalyze the reactions of the substrate. The importance of platinum metal complexes containing weak donor ligands in the homogeneous activation of organic substrates, which are themselves only modest ligands,'* is thus apparent. This present review describes the weak bonding in these complexes by use of a simple molecular orbital model essentially derived from the Lewis acid-base ' P r e n t address: Guel h Waterlm Centre for Graduate Work in Chemistry. Universityof&elph, Guelph, Ontario. NIG 2W1, Canada.
Julian A. Davles is a postdoctoral fellow at the @el+Waterloo
Centre for Graduate Work In Chemistry. He graduated from Im C o l b London wim a B.Sc. and ARCS h C h e w In 1976 and fmn Lha Royal W r y of Wnce wllh a Ph.D. h 1979. His research interests lie in the field of platinum metals chemlstry wim particular reference to homogeneous catalysis.
1-
definitions. The chemistry of platinum metal complexes containing weak donor ligands is outlined, divisions being made according t~ the nature of the weak donor and the applicability of the bonding model examined. Comments on preparative techniques and the relevance of such complexes in homogeneous catalysis are included. 11. Mefal-Llgend Interaclbns: An Approach to the Phenomenon of Weak Bondhg
The original acid-base defmition as s t a t d by Lewis1s
(".. .the basic substance furnishes a pair of electrons
for a chemical bond; the acid substance accepts such a pair") may be applied to a wide range of chemical interactions. In inorganic chemistry, all metal ions may
80 Chemical Reviews, 1981, Vol. 81, No. 1
Davies and Hartley
TABLE 1. Stability Series for Class a and Class b Acids for class a acids for class b acids ~~
N >> P > As > Sb > Bi 0 >> S > Se > Te F >> Cl > Br > I
N As > Sb > Bi 0
