Organometallics 1995, 14, 5442-5445
5442
Reactivity Studies of Tricyclohexylphosphine (PCy3) Square-Planar Iridium Complexes with Small Gaseous Molecules ( 0 2 , H2, Cl2, and S02). Molecular and Crystal Structure of Ir(C0)[OS(O)OH](so2)(Pcy3)2'c6.&, the First Structurally Characterized Oxygen-CoordinatedSOsH Complex Formed by Insertion of S02(g) into an M-OH Bond Cynthia A. Miller, Charles H. Lake, Melvyn Rowen Churchill," and Jim D. Atwood" Department of Chemistry, University at Buffalo, State University of New York, Buffalo, New York 14260-3000 Received June 1, 1995@ Summary: Square-planar iridium complexes of the large but strongly donating PCy3 (Cy = cyclohexyl) ligand, trans-Ir(CO)(Cl)(PCy3)2 and trans-Zr(CO)(OH)(PCydZ, have been reacted with the molecules 0 2 , Hz,Clz, and SOz. I n comparison to the analogous PPh3 complexes, the presence of PCy3 inhibits reactions with HZ and 0 2 but has little effect on reactions with Clz and SOz. Zn the latter two reactions the greater electron density compensates for the larger size of the PCy3 ligands. Reaction of SO2 with trans-Ir(CO)(OH)(PCy3)2 leads to a n oxygen-coordinated hydrogen sulfite ligand, and the structure was determined. The molecules exist in the crystals as weakly bound dimers.
Introduction Addition reactions to square-planar iridium(1) complexes have been a useful source for mechanistic information.1,2 Oxidative addition of molecules such as H2 and CH313s4 and binding studies of 025and alkenes2 have proved very useful for understanding the role of steric and electronic factors in such reactions. Complexes of the type trans-Ir(CO)(Cl)Lz, L = a phosphine ligand, have allowed variation of the electron density at the iridium. Such studies have shown that enhanced electron density at the iridium increases the rate of oxidative addition of CH3I: has little effect on oxidative addition of H2,3and enhances binding of 0 2 and SO2 t o the iridium enter.^,^ Relatively few studies have examined the reactivity of square-planar complexes of the strongly donating but large PCy3 ligand. A few complexes of nickel, palladium, and platinum have been reported, MXX'(PCY&.'-~ A rhodium complex, RhCI(S02)(PCy&,10 a n d its reac@Abstractpublished in Advance ACS Abstracts, October 15,1995. (l)Atwood, J. D. Coord. Chem. Reu. 1988,83,93. (2)Vaska, L. Acc. Chem. Res. 1968,I , 335. (3)Chock, P.B.;Halpern, J. J . Am. Chem. SOC.1966,88,3511. (4)Ugo, R.;Pasini, A.; Fusi, A.; Cenini, S. J.Am. Chem. SOC.1972, 94, 7364. (5) Lawson, H. J.; Atwood, J. D. J . A m . Chem. SOC.1989,111,6223. (6)Miller, C. A.; Janik, T. S.; Lake, C. H.; Toomey, L. M.; Churchill, M. R.; Atwood, J. D. Organometallics 1994,13, 5080. (7) Seligson, A. L.; Cowan, R. L.; Trogler, W. C. Inorg. Chem. 1991, 30, 3371. (8) Imoto, H.; Moriyama, H.; Saito, T.; Sasaki, Y.J . Organomet. Chem. 1976,126,453. (9)Darensbourg, D.J.;Wiegraffe, P.; Riordan, C. G. J . Am. Chem. SOC.1990,112,5759.
tion with oxygenll were described. In this manuscript the reactions of trans-Ir(CO)(PCy&X (X = C1 or OH) with H2, Cl2, 02, and SO2 are examined. Reaction of the hydroxo complex with SO2 leads to an oxygencoordinated hydrogen sulfite ligand. The hydrogen sulfite ion has been much discussed with regard t o the site of the proton, HS03- or S020H-.12-19 Observation of an S-H stretch demonstrated the presence of HS03-,12 which has been corroborated with crystal structure determinations.13J4 Evidence for S020H- in the presence of extra infrared modes in solution1' and from calculations has been presented.18 Oxygen-17NMR was used to show an equilibrium between the two isomers in water and indicated the more abundant isomer to be that with protonation on the oxygen.lg In the structure of Ir(CO)[OS(O)OHI(S02)(PCy3)2 we provide the first structural evidence for protonation of hydrogen sulfite on the oxygen and the first example of a hydrogen sulfite ligand coordinated through an oxygen.
Experimental Section IrC13.3Hz0 was purchased or borrowed from Johnson Matthey. Tricyclohexylphosphine was purchased from Strem Chemical Company. The gases, SOz, Hz, 10% SO2 in Nz, and 1.1%SO2 in Nz, were purchased from Matheson. Solvents were dried and purified by standard methods. All syntheses were accomplished under an argon or nitrogen atmosphere using an argon-filled glovebox or Schlenk or highvacuum techniques. Square-planar iridium complexes transIr(CO)(Cl)(PCy&and trun~-Ir(CO)(OH)(PCy3)2~ were prepared as previously described. 'H and 31PNMR spectra were recorded on a Varian VXR400. References were set to residual solvent peaks in the 'H (10)van Gaal, H. L. M.; Verlaan, J. P. J. J . Organomet. Chem. 1977,
~13.1. _ _93.
(ilYKubas, G. J. Inorg. Chem. 1979,18,182. (12)Maylor, R.;Gill, J. B.; Goodall, D. C. J. Chem. SOC.,Dalton Trans. 1972,2001. (13)Johansson, L.-G.; Lindqvist, 0.; Vannerberg, N.-G. Acta Crystallogr. 1980,B36, 2523. (14)Magnusson, A.; Johansson, L.-G.; Lindqvist, 0.Acta Crystallogr. 1983,C39, 819. (15)Meyer, B.; Peter, L.; Spitzer, K. Inorg. Chem. 1977,16, 27. (16)Guthrie, J. P. ACC.Chem. Res. 1983,16, 122. (17)Connick, R. E.;Tam, T. M.; von Deuster, E. Inorg. Chem. 1982, 21, 103. (18)Stromberg, A.; Gropen, 0.;Wahlgren, U.; Lindqvist, 0. Inorg. Chem. 1983,22,1129. (19)Homer, D. A,; Connick, R. E. Inorg. Chem. 1986,25,2414.
0276-733319512314-5442$09.00/00 1995 American Chemical Society
Organometallics, Vol. 14, No. 11, 1995 5443
Notes
(k
Table 1. Final Atomic Coordinates ~ 1 0 4 )and NMR spectra. 31PNMR spectra were referenced to an external x 109 for Isotropic Displacement Coefficients at 0.0 ppm and are proton decoupled. All sample of Ir(C0)[OS(O)OHl(SO2)(PCYS)Z.CSH~ chemical shifts are reported in ppm and all coupling constants (J)are reported in Hz. Infrared spectra were obtained using atom X Y z UeqP a Mattson Polaris Fourier Transform spectrometer with 0.5 758(1) 2452(1) mm NaCl solution cells or KBr disks. Elemental analysis was 3391(2) 1607(2) 2086i2j done a t E & R Microanalytical. 4003(2) 369(2) 427(2) Ir(CO)[OS(O)OH](SO2)(PCy& Crystallization.20A sus3951(2) -441(1) 2585(1) pension of 0.210 g of trans-Ir(CO)(OH)(PCy3)2 in 15 mL of 5704(1) 1703(1) 2383(1) benzene was prepared in an argon atmosphere. The reaction 5009(5) 4232(4) 1043(5) 3406(6) 2706(6) 2109(6) vessel was sealed and transferred to a hood. The mixture was 3193(9) 1298(6) 1724(8) refluxed under a N2 atmosphere for 5 min, causing it to 4638(4) 1264(3) 502(4) completely dissolve. The reaction mixture was then cooled to 4177(5) -493(4) 234(4) 0 "C, and SO2 was bubbled through it for 15 min, followed by 4339(6) 860(5) -1406) stirring at 0 "C under an SO2 atmosphere for another 15 min. 875(54) 4907(65) -60(56) Next, the homogeneous mixture was layered with an S02948(5) 3542(6) 4867(6) saturated heptane solution and placed in a refrigerator -823(5) 1650(6) 3166(6) overnight. No crystals resulted, so the volume of the solution 1565(7) 3051(6) - 1702(6) was reduced by the addition of SO2 while allowing it to warm 2488(6) -1935(6) 716(7) 1638(7) -1505(6) 510(7) to room temperature. After 24 h at room temperature yellow1768(7) -618(6) 591(7) green crystals resulted. IR (KBr):vco= 1939 cm-', YSO = 1078 2330(6) -390(6) 1445(6) and 940 cm-' for the hydrogen sulfite, and the other S-0 4751(6) -1227(5) 2885(6) stretches are obscured by the cyclohexyl absorbances. 31P 5238(7) -1309(7) 2250(8) NMR (CD2C12): 8.4 ppm. The crystals were suitable for X-ray 5844(8) -2006(8) 2453(11) crystallography. Anal. Calcd: C, 46.63; H, 7.25. Found: C, 6432(9) -1937(10) 3277(14) 47.98; H, 7.29. 5981(9) -1844(8) 3937(11) Reaction of H2 with Ir(CO)[OS(O)OHI(S02)(PCys)z. In 5384(8) -1132(7) 3730(7) 3486(7) -456(6) an argon atmosphere, a dilute solution of trans-Ir(CO)(OH)3448(6) 2950(7) 3489(7) 253(7) (PCy& in toluene was prepared. The Schlenk flask was 2734(8) 4310(7) 230(8) equipped with a gas adapter, sealed, and transferred t o a hood. 2277(10) 4377(9) -507(10) In the hood 1.1%SO2 in Nz was passed over the solution for 2 2783(10) 4331(8) -1226(10) h. An IR spectrum of the bright yellow solution showed one 3053(7) -1229(7) 3542(6) absorbance, YCO = 1935 cm-l, attributed t o Ir(CO)[OS(O)OHl6062(6) 3296(5) 2345(5) (SO2)(PCy3)2. Hydrogen gas was passed over this solution for 6852(6) 3397(6) 2820(6) 2 h more, and another infrared spectrum was recorded, 7171(7) 4243(6) 3179(6) showing no evidence of Ir(CO)[OS(O)OH)(S02)(PCy3)2 or trans6518(7) 4427(6) 3687(6) 5694(7) 4297(7) 3236(7) Ir(CO)(OH)(PCy&. The toluene was removed in vacuo, and 5381(7) 3445(7) 2885(7) the yellow powder was transferred to an argon atmosphere 6681(6) 2456(5) 1162(5) where it was dissolved in CD2C12. A IH NMR spectrum was 7057(7) 729(6) 3262(6) recorded showing resonances in the hydride region a t -12.1 7910(8) 3320(7) 360(8) ppm (td) [2Hl J = 14.8, 5.6; -12.8 ppm (tt) [lH] J = 20, 5.6; 7856(8) 2615(7) -154(7) -9.9 ppm (td) [ l H ] J = 16.4, 3.6; and -18.4 ppm (td) [lH] J 7500(7) 1817(7) 265(8) = 16.4, 3.6. The resonances a t -12.1 and -12.8 ppm are 6614(7) 1740(6) 598(6) assigned to mer-H&(CO)(PCy3)2,22and the -9.9 and -18.4 1412(5) 5473(5) 2273(5) ppm resonances are assigned t o H~Ir(CO)[OS(O)OHI(PCy~)~ 6225(8) 1204(8) 2604(9) 5966(9) 2952(10) 336(8) on the basis of NMR shifts, coupling patterns, and coupling 5273(9) 3531(9) 196(8) constants. 3229(11) 443(10) 4572(9) Collection of X-ray DiffractionData for Ir(CO)[OS(O)1300(9) 4828(10) 2888(9) OH](S02)(PCy&C,&. A single yellow-green crystal (di2564(16) 6436(9) 3840(10) mensions 0.15 x 0.15 x 0.20 mm3) was inserted into a thin4081(15) 6239(15) 3355(17) walled glass capillary and aligned on an upgraded Syntex P21/ 5812(22) 3613(14) 4730(17) Siemens R3 diffractometer. The crystal belongs t o the 5491(17) 3151(24) 5127(15) monoclinic system. The systematic absences h01 for h 1 = 5654(15) 2358(19) 4879(16) 4233(12) 6155(15) 2068(9) 2n 1 and OK0 for K = 2n 1uniquely define the centrosymmetric monoclinic space group P21/n. All data were corrected a Equivalent isotropic U defined as one-third of the trace of the for Lorentz and polarization effects and for absorption. Crystal orthogonalized Uu tensor. data: C ~ ~ H ~ , I ~ O ~ P Zmonoclinic, S ~ * C ~ Hs ~ace , group P21/n (No. 14), a = 16.7164(27)A, b = 16.9954(25) c = 17.1373(28)A, difference-Fourier methods. All non-hydrogen atoms were ,8 = 107.578(12)", V = 4641.4(13) A3, 2 = 4, fw = 1004.35 located (as was H(6), the hydrogen atom of the -OS(O)OH , 3.079 mm-', 6103 (926.24 78.111, D = 1.438 g ~ m - p~ = ligand, which was subsequently refined), and hydrogen atoms reflections, 3854 > 6a(F), R = 3.61 and wR = 3.83 for 60 data, of the tricyclohexylphosphine ligands were included in calcuand R = 6.93 and wR = 6.19 for all data. lated positions (their U values each being defined as equal to Solution and Refinement of the Structure. All crystalthat of the U(equiv) value of the carbon atom to which they lographic calculations were performed with use of the Siemens were attached). Refinement converged = 0.004 with SHELXTL PLUS program set on a VAXstation 3100 computer R = 3.61 for those 3854 reflections above 6dF) and R = 6.93 system. Scattering factors for neutral atoms were corrected for all 6103 independent data. Final atomic coordinates are for both components ( A f and i A 7 ) of anomalous dispersion. collected in Table 1. The structure was solved by a combination of Patterson and
+
+
+
1,
+
(20)This procedure follows closely that previously reported for crystallizing Ir(CO)(I)(S02)2(PPh3)2.2l (21)Snow, M. R.;Ibers, J. A. Inorg. Chem. 1973,12,224. (22)Harrod, J. F.;Yorke, W. J. Inorg. Chem. 1981,20,1156.
Results Reactions. The PCy3 complexes show reduced reactivity in comparison with their PPh3 analogues,1,2
5444 Organometallics, Vol. 14, No. 11, 1995
Notes
with no reaction observed between trans-Ir(CO)(Cl)(PCy3)2 and H2 or 0 2 after 1 and 4 days, respectively, at 25 "C in cyclohexane. However, the complex does retain reactivity toward Cl2 and SOZ, the reactions complete in under 10 Reactions of the hydroxy complex, trans-Ir(CO)(OH)(PCy3)2, with HZand 0 2 occur only to the extent of 5% after 1 and 4 days, respectively, forming Ir(CO)(H)3(PCy& (YCO = 1934 cm-l, Y I ~ H= 2035,1787 cm-') and Ir(CO)(Oz)(OH)(PCy3)z (YCO = 1930 cm-l), respectively. In both cases the starting complex trans-Ir(CO)(OH)(PCy312 was present (-95%) after 4 days at room temperature. These products are those expected on the basis of reactions of the PPh3 analoguez5but are formed in much less quantity. Reaction of SO2 with trans-Ir(COXOH)(PCy3)2produces two products depending on the conditions employed. Reaction with 1atm of SO2 in toluene produces a product with a single YCO at 1997 cm-l and a single 31Presonance a t 18 ppm. Neither free PCy3 nor any evidence of an Ir-H was observed. Workup (as described in the Experimental Section) produced Ir(C0)[OS(O)OHI(SOZ)(PC~~)Z with a YCO at 1939 cm-l and a 31Presonance at 8.4 ppm. The complex Ir(CO)[OS(O)OHI(S02)(PCy& was formed as the sole product by reaction of Ir(CO)(OH)(PCy3)2with 1%SOz in an NZgas mixture. To assist in interpreting these products a was crystal structure of Ir(CO)[OS(O)OHI(S0~)(PCy~)~ determined. Crystal Structure of Ir(C0) [OS(O)OHl (Sod(PCys)2*C&. The crystal consists of ordered molecand benzene ular units of I~(CO)[OS(O)OHI(S~Z)(PC~~)~ of solvation in a 1:l ratio. The crystallographic asymmetric unit is shown in Figure 1. Selected interatomic distances and angles are collected in Table 2. The crystal packing is stabilized by hydrogen bonding between the OS(0)OH units of adjacent molecules. Thus, the defined molecule interacts with that related by inversion (about l/2 0,O)such that H(6)-0(5a) = H(6a).-0(5) = 1.77(11) with 0(6)--0(5a) = 0(5)-*0(6a)= 2.610(11) A and L0(6)-.H(6)-*0(5a) = L0(6a)-H(6a)-.0(5) = 151(8)". This is clearly shown in Figure 2. The iridium complex is related to a previously studied species, Ir(CO)[OS(O)OMel(SO~)(PPh~)~~0.5 (toluene),24 but now has the previously uncharacterized OS(0)OH ligand and PCy3 ligands. The iridium(1) atom has a square-pyramidal coordination geometry with the SO2 ligand in the apical site. The Ir(l)-S(l) bond length is 2.493(3) A (cf. 2.451(2)A in the OS(0)OMePPh derivative cited above). The sulfur atom has a pyramidal geometry (with, presumably, a lone pair of electrons). Bond lengths are S(1)-0(2) = 1.35601) and S(1)-0(3) = 1.305(11)A, while interatomic angles are Ir(l)-S(l)O ( 2 ) = 110.8(4)", Ir(l)-S(l)-O(3) = 106.2(7)", and 0(2)-S(1)-0(3) = 130.8(8)". We should note that dimensions in the , 9 0 2 ligand vary significantly from those for the SO2 ligand in the OS(O)OMePPh3derivative in which S-0 = 1.435(7)and 1.437(4)A and LO-
A
~
-
~~~
~~~
(23)The trichloro complex was characterized only by the shift in vco (1933 2033 cm-') upon Clz addition. This shift is very similar to the shift for the PPh3 analogue upon reaction with Clz (1955 2075 cm-lL2 The SO2 adduct was characterized by its YCO (1991cm-l) and its 31PNMR resonance (14.9ppm). Each is in the expected location
-
based on the P@-tolyl)3ana10gue.e~ (24)Randall, S.L.;Miller, C. A.; See, R. F.; Churchill,M. R.; Atwood, J. D. Organometallics 1994,13, 141. (25)Thompson, J. S.;Randall, S. L.; Atwood,J. D. Organometallics 1991,10, 3906.
Q
Figure 1. Atomic labeling for the basic asymmetric unit of I~(CO)[OS(O)OHI(S~Z)(PC~~)Z~C~H~. ORTEP2 diagram with 20% probability contours for non-hydrogen atoms and with hydrogen atoms artificially reduced. Table 2. Selected Interatomic Distances (A) and Angles (deg) for Ir(CO)[OS(O)OHl (S02)(PCy&C,$& Ir(l)-P(l) Ir(l)-P(2) Ir(l)-S(l) S(1)-0(2) S(2)-0(4) S(2)-0(5) S(2)-0(6) 0(6)-H(6) P(l)-Ir(l)-P(2) P(l)-Ir(l)-S(l) P(l)-Ir(l)-0(4) P(l)-Ir(l)-C(l) P(2)-Ir(l)-S(l) Ir(l)-S(1)-0(2) Ir(l)-S(l)-O(3) Ir(l)-0(4)-S(2) 0(4)-S(2)-0(5) 0(4)-S(2)-0(6)
2.408(3) 2.392(3) 2.493(3) 1.356(11) 1.521(6) 1.549(8) 1.511(10) 0.920 1) 163.9(1) 95.8(1) 92.9(2) 89.7(3) 100.2(1) 110.8(4) 106.2(7) 139.6(4) 102.7(4) 103.6(4)
Ir-0(4) Ir-C(l) C(1)-0(1) S(1)-0(3) 0(5a).-.H(6) 0(5a)**.0(6) 0(5)-.0(6a) P(2)-1r(1)-0(4) P(2)-Ir(l)-C(l) S(l)-Ir(l)-O(4) S(l)--Ir(l)-C(l) 0(4)-1r(l)-C(l) 0(2)-S(1)-0(3) 0(5)-5(2)-0(6) S(2)-0(6)-H(6) 0(6)-H(6)*-0(5a)
2.068(6) 1.826(10) 1.143(12) 1.305(11) 1.77(11) 2.610(11) 2.610(11) 84.0(2) 91.2(3) 96.3(3) 91.9(3) 171.1(4) 130.8(8) 104.7(5) 119(6) 151(8)
S-0 = 113.8(3)". It is possible that the shorter S-0 distances in the present molecule are an artifact of the larger thermal motions of this group. The -OS(O)OH ligand is associated with the following distances: 0(4)-S(2) = 1.521(6),S(2)-0(5) = 1.549(8), S(2)-0(6) = 1.511(10), and 0(6)-H(6) = 0.92(11) A. It is surprising that the S(21-06) distance (formally an S-0 linkage) is indistinguishable from the S(2)O(6) distance (an S-OH linkage). Either this is a result of intermolecular hydrogen bonding (see above) or there could be some disorder of S=O and S-OH linkages, concerning hydrogen bonding, which we have been unable t o detect. Angles around the chiral pyramidal sulfur(IV) atom S(2) are 0(4)-S(2)-0(5) = 102.7(4), 0(4)-S(2)-0(6) = 103.6(4), and 0(5)-S(2)-0(6) = 104.7(5)". Other features in the molecule are normal; the cyclohexyl rings in the PCys ligands have a chair conformation, with the phosphorus atoms occupying equatorial sites on one of the four coplanar carbon atoms which define the "seat" of the chair. Sulfur dioxide insertions into metal hydride,26metal
Notes
Organometallics, Vol. 14,No. 11, 1995 5445
n
Pa
ob
Figure 2. Hydrogen bonding between the defined unit and that with coordinates related by inversion about V 2 , 0, 0 (labeled with suffix “a”). This view also shows the squarepyramidal coordination geometry about iridium. Note that atom P(1) is hidden from view behind Irtl). alkyl,27and metal alkoxide have been reported. Insertion into a hydride produced the SO2H complex for CpMo(C0)3H; reaction with Cp*Ru(C0)2H produced a sulfur-coordinated S03H (hydrogen sulfite) ligand through a disproportionation reaction.26 A sulfurcoordinated hydrogen sulfite (CpFe(C0)2S03H)was also obtained by hydrolysis of CpFe(CO)2S03Me.27 Reaction of SO2 with truns-Ir(CO)(OH)(PCy3)~ provides the first example of insertion of SO2 into a metal hydroxide producing oxygencoordinated hydrogen sulfite. It is likely that steric constraints prevent the remangement of the oxygen-coordinated to the presumably more stable sulfur-coordinated hydrogen sulfite ligand. The complex formed, I~(CO)[OS(O)OH~(SOZ)(PC~~)~, is quite similar t o the kinetic product of the addition of SO2 t o tr~ns-Ir(CO)(OR)(P(p-tolyl)~)~.~~ Two aspects of the OS(0)OH- ligand are unique for hydrogen sulfite: (1) The proton is located on an oxygen instead of the sulfur. While infrared17 and 170NMRlg evidence for the existence of the oxygen-protonatedisomer of hydrogen sulfite prohas been presented, Ir(CO)(SOz)(OS(O)OH)(PCy3)z vides the first structural evidence. (2) In the two other examples in which hydrogen sulfite is a ligand in organometallic complexes, the ligand is coordinated through the sulfur t o the metal. Thus, for the OS(0)OH ligand reported herein the pair of electrons on sulfur is stereochemically active, but does not participate in bonding t o the proton or to the iridium. Possibly the oxygen coordination to the iridium reduces the steric interactions, and the protonation on the oxygen allows extra stability from intermolecular hydrogen bonding (26) (a) Kubat-Martin, K. A.; Kubas, G. J.; Ryan, R. R. Orgammetullics 1989,8, 1910. (b) Kubas, G. J.;Wasserman, H. J.;Ryan, R. R. Organometallics 1985, 4 , 2012. (27)(a)Kroll, J. 0.;Wojcicki, A. J. Orgunomet. Chen. 1974, 66, 95 and references therein. (b) Hartman, T. A.; Wojcicki,A. J.Am. Chem. Soc. 1966,88, 844. (c) Poffenberger, C. A.; Wojcicki, A. Inorg. Chem. 1980,19, 3795.
(Figure 2). Regardless of the rationale, the OS(0)OHligand is highly unusual. When 10% SO2 in NS or greater concentrations are used, an intermediate is formed that rearranges to Ir(CO)[OS(O)OHI(S02)(PCy3)2upon workup. Two possibilities for this species (YCO = 1997 cm-l and a 31P resonance a t 18.0 ppm) cannot presently be discerned: (1) A species is formed containing either SO2 bound differently (coplanar instead of pyramidally, for instance) or hydrogen sulfite bound through sulfur. It is difficult to rationalize that, if the sulfur-coordinated HSO3- could form, the soft sulfur ligand would rearrange to the harder oxygen coordination for the sulfite. A change in coordination of the SO2 is quite possible, though how this could be affected by the concentration of SO2 is not readily apparent. (2) A third SO2 could coordinate, possibly reversibly inserting into the iridium-oxygen bond of the sulfite ligand or coordinating to the oxygen of the hydrogen sulfite ligand. The Ir-0 bond of the coordinated sulfite ligand may not be very different from that of the Ir-0 from the hydroxide. These reactions would be similar to the known reactions of HS03- forming bisulfite S Z O ~ ~in- this ; case, HS03SO2 HS2O5-. On the basis of the positions of the 31Presonance and the infrared frequency and on the formation only a t higher concentrations of S02, the second is more likely, but our inability to isolate this product precludes assigning a structure. While truns-Ir(CO)(OH)(PCy3)~ does not react with Hz, the five-coordinate hydrogen sulfite complex reacts readily forming two iridium-containing products.
+
-
+
Ir(CO)[OS(0)OHI(S0,)(PCy3~, 2H, ner-Ir(CO)(H),(PCy3),
-+ H,O + 2S0,
The ultimate product, mer-Ir(CO)(H)3(PCy3)zthas the characteristic triplet of doublets and triplet of triplets splitting with the appropriate coupling.25 This is the product observed when many trans-Ir(CO)(R)Lz complexes react with H2.1925The second product, formed at intermediate times and not isolated, has two triplets of doublets in a 1:l ratio characteristic of iridium cis dihydride complexes. We assign this product as Ir(C0)(H)2[0S(O)OHI(PCy3)2.That electronic effects and not just steric factors are important is further shown by the fact that Ha reacts with truns-Ir(CO)(CH3)(PCy3)~.
+
truns-Ir(CO)(CH3)(PCy3), H, Ir(CO)(CH,)(H),(PCy,),
-+
Ir(CO)(H),(PCy,),
The methyl complex is not significantly smaller than the chloro complex.
Acknowledgment. We are grateful t o the National Science Foundation for funding the upgrade and purchase of our diffractometers (Grant 89-13733 from the Chemical Instrumentation Program). Supporting InformationAvailable: Complete tables of distances, angles, anisotropic thermal parameters, and calculated hydrogen atom positions for I~(CO)[OS(O)OHI(SOZ)(PCYs)z’CsHs (5 pages). OM950410+
