Carbonyl Complexes of Osmium TRIOSMIUM DODECACARBONYL and ITS DERIVATIVES

Carbonyl Complexes of Osmium TRIOSMIUM DODECACARBONYL AND ITS DERIVATIVES

By C. W. Bradford, B.s~. Research Laboratories, Johnson Matthey & Co Limited

The study of the carbonyls of most of the platinum metals has led to the preparation of a whole series of new complexes, some of which have potential usefulness in the$eld of homogeneous catalysis. In the case of osmium carbonyls, however, research has so far been hampered by di#- culties in their preparation. The new method of preparation described here now makes it possible to investigate the chemistry of osmium complexes along the same lines.

In recent years there has been a tremendous have resulted in very variable and very low advance in the chemistry of the transition yields, and, in the case where osmium tetr- metals including those of the platinum group oxide was the starting material, the formation metals. The preparation and study of car- of large quantities of black decomposition bony1 complexes has proved most fruitful, and products. A new procedure (3, 4) has now it is hoped that further investigation of been developed in these laboratories which reactions involving the carbonyls may result results in the production of Os,(CO),, in in the discovery of compounds having useful good yields (70 per cent) and, as a by-product, properties, particularly in the field of homo- the oxycarbonyl, Os,Op(CO),, (5). A solu- geneous catalysis. An improved method has tion of osmium tetroxide in xylene is heated now been developed for the preparation of at 175°C for 16 hr in an autoclave containing triosmium dodecacarbonyl, Os,(CO),,, and carbon monoxide at a pressure of 190 some of its reactions have been studied. atmospheres. The large yellow crystals of Os,(CO),, are readily separated by hand Preparation of Osmium Carbonyls from the white oxycarbonyl Os,O,(CO),, In 1943 Hieber and Stallman (I) produced and both compounds are finally purified carbonyls of osmium by the action of carbon by recrystallisation from bcnzene. In the monoxide at high pressure either on osmium presence of xylene there are no signs of the tetroxide or on osmium trihalides in the decomposition products which appear when presence of silver or copper powder to take the reaction is carried out in its absence. up the halogen. They separated two pro- ducts, a volatile colourless liquid (m.p. Reactions of Os,(CO),, - 15'C) and a yellow crystalline solid claimed When OS,(CO),~is reacted in hot xylene respectively to be Os(CO), and Os,(CO),. solution with triphenylphosphine [P(Ph),] An X-ray examination (2) of the latter has, in and with o-phenylenebisdimethylarsine fact, shown it to be Os,(CO),,, the molecule (Diars) the substitution products [Os(CO), having three osmium atoms at the corners of PPh,], and [Os(CO),Diars], are formed. In an equilateral triangle, each osmium atom both cases molecular weight determinations having four terminal CO groups, two ap- by osmometry have confirmed that the tri- proximately perpendicular to and two parallel nuclear metal cluster in the original carbonyl to the plane of the triangle, Attempts to pro- has been retained in the derivatives. This is duce the carbonyls by either of these routes similar to the behaviour of the analogous

Platinum Metals Rev., 1967, 11, (3), 1044105 104 Triosmiiun Dodecacarbonyl and Some of its Derivatives

Infra-red C 0 Stretching Molecular Weight - Compound Colour Found Frequencies, cm-l (in Nujol Mull)

907 2070(S), 2041(Sh), 2028(Sh), 2019(S), 1998(M), 19WW *2066(S), 2033(S), 2012(M), zooo(M) 1161 OS,O,(CO),, White 1610 [Os(CO)Ph,l, Orange-red [Os(CO),Diars], Brownish-yellow 1474 I597 Os(CO),(PPh,)Cl,[Os(CO),Diars], White Brownish-yellow 712 607

Os(CO),(PPh,)Br, Light yellow 798 698

Os(CO),(PPh,)I, Golden yellow 790 Impure (CO),(PPh3)CIOs-HgC1 White 808

(CO),ClOs-HgCl Light yellow-green 606 574 *In chloroform solution ruthenium carbonyl, Ru,(CO),,, with tri- have been prepared directly from Os,(CO),,. phenylphosphine (6). Cleavage of the metal- Further work on the reactions of the metal bonds is, however, achieved if osmium carbonyl and its derivatives with [Os(CO),PFh,], is reacted in benzene soh- halogens, halogen acids and mercuric halides tion with halogens, and compounds of the is proceeding and will be reported in due type Os(CO),PPh,X,, where X =C1, Br, or I, course. have been isolated. The author’s thanks are due to Professor Both the parent carbonyl and the triphenyl- R. S. Nyholm for guidance and encourage- phosphine derivative react with mercuric ment in this work. chloride to yield interesting new compounds containing 0s-Hg bonds. The former reacts References in hot xylene solution to yield (CO),CI I W. Hieber and H. Stallman, Z. Elektrochern., 0s-HgC1 and the latter in cold benzene 194314%288 2 E. R. Corey and L. F. Dahl, Znorg. Chern., 1962, solution to yield (CO),(PPh3)C10s-HgC1. 1,521 Similar Os(0) and Os(I1) complexes, e.g. 3 C. W. Bradford and R. S. Nyholm, Chem. Cornm., 1967, 384 Os(CO),(PPh,) and Os(C0) *(PPh,) $3,have 4 C. W. Bradford, Johnson Matthey, British been reported by Collman and Roper (7), Patent Appln. oo221/1967 who have also prepared cationic complexes 5 B. F. G. Johnson, J. Lewis, I. G. Williams and containing 0s-Hg bonds, e.g. [(CO),(PPh,), J. Wilson, Chem. Comm., 1966, 391 6 J. P. Candlin, K. K. Joshi and D. T. Thompson, 0s-HgClIHgC1, (8). However, these com- Chem. and Ind., 1966,1960 pounds were produced by an entirely differ- 7 J. P. Collman and W. R. Roper,J. Amer. Chem. ent route and the derivatives listed, together SOC., 1966, 88, 3504 8 J. P. ColIman and W. R. Roper, Chem. Cm., with some of their properties, are the first to 1966,244

Platinum Metals Rev., 1967, 11, (3) 105