Organometallics 1988, 7 , 1093-1100
1093
Synthesis and Reactivity of Mercury-Bridged Transition-Metal Clusters. 4.'" Reactivity of (p,-q2-C2-t-Bu) (CO)gRu3HgMo(q5-C,H5) (CO), Edward Rosenberg" and Jiandang Wang Department of Chemistry, California State University, Northridge, California 9 1330
Robert W. Gellert Department of Chemistry, California State University, Los Angeles, California 90032 Received August 3, 1987
The thermolysis, photolysis, and phosphine substitution reactions of [Ru3!p3-$-C2-t-Bu)(CO),](paHg)[Mo(q6-C6H,)(CO),](I) and ita derivatives have been studied. Redistribution reaction between the two different monophosphine-substituted derivatives of I show that the Hg-Mo bond is relatively labile compared to the r-Hg-Ruz bond. Photolysis of I yields the product (p~-~2-C2-t-B~)R~~Mo(~5-C5H5)(CO)~ (VII), a new triangular mixed-metal cluster. The solid-state structure of VI1 was determined by X-ray crystallography. Compound VI1 crystallizes in the monoclinic space group P2Jc with a = 9.116 (2) A, b = 15.982 (3)A, c = 13.510 (5) A, p = 108.81 (2)O,V = 2139.1 (8) A3, and dcalcd= 2.075 g/cm3 for 2 = 4. Least-squares refinement led to final agreement indices R = 0.018 and R, = 0.024 for 3217 observed reflections. An investigation of the ligand dynamics of VI1 by variable-temperature 13C NMR revealed that there is no intermetallic scrambling of carbonyls around the RuzMo triangle, but a restricted edgehopping motion of the coordinated acetylide between the two Ru-Mo edges is observed. Introduction We have been studying the synthesis and reactivity of mercury-mixed transition-metal cluster^.^-^ One of the goals of this research is to elucidate the fundamental differences between the well-known two-center, two-electron mercury-transition-metal bond and the more recently reported p-, p3-, and p4-electron-deficient transition metal-mercury bonds. We recently reported the results of such a study comparing the chemistry of [(p3-$-Cz-tB~)(C0)&u~]~(p,-Hg) (II)with M-Hg-M (M = transition metal) system^.^ We report here a related study on the compound [ (p3-q2-Cz-t-Bu) ( C O ) 9 R ~ (p3-Hg) 3] [Mo(05C5H5)(C0)I3(I) where a comparison of the normal covalent
and electron-deficient mercury transition-metal bonds can be compared in the same molecule. A second goal of this research is to utilize the known photoreactivity of mercury to synthesize heterometallic bonds by photoinduced reductive elimination of mercury. While we previously found I1 to be photochemically inactive? we report here that I undergoes not only an apparent elimination of mercury but also a regiospecific replacement of one Ru atom by the Mo atom in the original Ru, triangle of I. (1) (a) For parta 1-3 see ref 2-4 below. (b) Rosenberg, E.; King, K.; Fahmy, R.; Tiripicchio, A. J . Am. Chem. SOC.1980, 102, 3626. (2) Roeenberg, E.; Hardcastle, K.; Ermer, S.; King, K.; Tiripicchio,A. Inorg. Chem. 1983,22, 1339. (3) Rosenberg,E.; Ryckman, D.; Gellert, R.; Hsu, I. Znorg. Chem. 1986, 25,194. (4) (a) Novak, B. Masters Thesis, California State University, Northridge. (b) Rosenberg, E.; Novak, B. Organometallics, submitted for publication.
Results and Discussion A. Thermolysis of I. [ R u ~ ( ~ ~ - T ~ - C(CO),] ~ - ~ -(p3BU) H ~ ) [ M O ( ~ ~ - C ~ H , ) ( (I) C Ois) ~relatively ] stable toward thermal decomposition. Nevertheless, refluxing I in solvents of boiling point lower than 100 OC under Nz atmosphere for 20 h resulted in the formation of some H[RU~~-~~-C~-~-BU 11:) (and C OHg[(Mo(ll-C,H,)(CO),Iz )~I, (III), each of which was identified by TLC, IR, and lH NMR (eq 1). From the yield data shown in eq 1, two
THF (67%)
(heptane) (80)
10% (3.5)
I1 6.6% (6.5)
I11 15 %
(9.2)
( 5 ) Mays, M. J.; Pearson, S. M. J. Chem. SOC.A 1968, 68, 2291.
0276-733318812307-1093$01.50/0 0 1988 American Chemical Society
1094 Organometallics, Vol. 7, No. 5, 1988
Rosenberg et al.
Table I. Spectroscopic and Analytical Data for Compounds Reported I IV V VI
mol mass infrared (methylene chloride) (cm-*) (-C=O)
'H NMR (chloroform-d) (ppm) -CH3 45H5 -CBH5 31PNMR (chloroform)a (ppm) (Mo)-PPh, (Ru)-PPha mass spectra (amu) mol ion elemental analysis (%) found C found H calcd C calcd H a
1082.10
1316.38
1316.38
2075 (w) 2025 (s) 1993 (s) 1985 (s) 1915 (m) 1890 (s)
2085.5 2080.8 2053.7 2040.8 2001.3 1936.0 1906.5 1881.9 1821.0
1.40 (9, s) 5.29 (5, s)
1.42 (9, s) 5.33 (5, s) 7.44 (15, m)
(w) (w) (m)
2079.5 2050.0 2043.7 2007.8 1888.5 1824.2
(s) (8)
(w) (m) (m) (w)
VI1
1550.66
(m)
2055.1 2035.3 1998.2 1986.5 1966.0 1936.0 1886.5 1821.2
(s)
(s) (s)
(w) (m)
668.39
(m)
2071.9 2037.0 2000.3 1967.6 1903.9
(s) (s) (s)
(m) (w) (w) (m)
1.40 (9, s) 4.92 (5, d) 7.38 (15, m)
1.42 (9, s) 4.93 (5, d) 7.41 (15, m)
81.42 (s)
81.74 ( 1 P,s) 64.85 ( 1 P, s)
64.80 (s)
(s)
(m) (w)
1.41 (8, s) 5.34 (5, 9)
1082 25.87 1.74 25.53 1.50
(s) (s)
668 36.80 2.26 36.50 2.22
36.62 2.36 36.50 2.22
43.85 2.99 44.15 2.86
34.19 1.01 34.14 0.91
31PNMR chemical shifts are reported downfield positive relative to external 85% H3P04(uncorrected for bulk susceptibility).
points can be made: first, a larger percent of the starting material decomposes, overall, in tetrahydrofuran than in heptane despite the fact that heptane has a boiling point 31 degrees higher than that of THF; second, the yield of the hydrido cluster is lower than that of I1 in the heptane reaction whereas the yield of I1 is lower in the THF reaction. Redistribution reactions involving homolytic and heterolytic bond cleavages and/ or bimolecular intermediates could lead to the formation of I1 and 111. Although products assignable to cleavage of both types of Hg-metal bonds in I are observed, their relative rate of cleavage is not revealed by these experiments. The formation of the hydrido cluster suggests the formation of Ru3 radicals that then abstract hydrogen from the solvent. B. Phosphine Substitution Reactions on I. Triphenyl, trimethyl, and other phosphines substitute for one or two CO ligands in compound I1 with relative ease.4 Starting material was usually consumed within a few hours. The phosphine substitutes for one carbonyl on the wing-tip Ru atom in one triangle of I1 to form a monosubstituted product followed by a second substitution on the analogous Ru atom of the second triangle in refluxing toluene. [Mo(~~-C,H,)(CO),]~H~ (111)also readily undergoes bis(phosphine) substitution at each Mo atom., When a solution of I is refluxed with triphenyl- or trimethylphosphine at 65-100 " C , two different mono(phosphine)-substituted derivatives of I are observed to be the initial products formed. These products, IV and V, have Rf (TLC, silica gel) values very close to one another and were difficult to separate. Both products (IV and V) show IH NMR resonances for the tert-butyl methyl groups, the cyclopentadienyl group, and the alkyl or aryl groups of the phosphine ligand in a 1:l:l stoichiometric ratio (see Table I). The chemical shifts of analogous resonances were different for IV and V. The product with a greater Rf value (V) has a cyclopentadienyl resonance that appears as a doublet (J= 1.1Hz). This is assigned to a three-bond proton-phosphorus coupling, suggesting that in this isomer, the phosphine is bound to the Mo atom.6 Product (6) Kubicki, M. M.; Kergoat, R.; Gall, J. X. L.; Guerchais, J. E.; Douglade, J. Aust. J. Chem. 1982, 35,1343.
IV, on the other hand, has a singlet resonance for its cyclopentadienyl group. The 31PNMR spectrum for V shows a single peak at 81.42 ppm (with respect to H,P04, 6 0) and two Hg satellites arising from a Hg-P two-bond coupling (2J(1g9Hg-31P)= 278 Hz). IV also gave a singlet in its 31PNMR spectrum at 64.80 ppm but with no satellites. The latter chemical shift is identical with that observed for mono- or bis-substituted phosphine derivatives of I1 where the phosphine substitutes on one (64.89 ppm) or both (64.51 ppm) of the wing-tip rutheniums, respectively: When a phosphine substitutes on one of the ruthenium atoms bridged to the Hg in 11, the 31PNMR resonance was found at 44.89 ppm with two mercury satellites due to the two-bond coupling (2J(1g9Hg-31P)= 573.6 H z ) . ~Therefore, the phosphine is substituted on the wing-tip ruthenium atom in IV and on the molybdenum atom in V. At longer reaction times, a low Rr product, VI, is observed. The lH NMR of this product shows a relative intensity of 30:9 for the phenyl and tert-butyl methyl protons, respectively. The 31PNMR spectrum contained two resonances of equal intensity at 64.85 (no satellites) and 82.74 ppm (2J(lg9Hg-,lP) = 271 Hz). This leaves no doubt that VI is a bis(phosphine) substitution product of I where one phosphine substitutes on each metal moiety (eq 2). Attempts
Ru
9"
R< \Hg--Mo-PPh3 \Ru/
v (18 %)
+
PhBP-R
