Organometallics 1983,2, 459-460
forces on the overall electronic structure of the complex should be minimal. Despite the apparent dissimilarity between the free carbene and the protected system studied here, the Tebbe reagent effectively mimics the known chemistry of alkylidene complexes. Since the theoretical structure of 2 suggests that it is very strongly bound, it seems unlikely that the similarity arises from formation of a highly reactive free alkylidene complex via unaided equilibration with the Lewis acid. More likely, an incoming substrate or solvent molecule (or both) displaces the Lewis acid in a concerted fashion. G r u b b P has noted that extremely bulky Lewis bases facilitate the formation of titanacyclobutanes from 1 and olefins, implying that the Lewis acid fragment is removed by the base. Exploration of these possibilities via further theoretical work is in progress. Registry No. 1, 67719-69-1.
Reactlon of HCi with Photoproduced Base-Substituted Manganese Carbonyl Radlcals Blaine H. Byers," Timothy P. Curran, Michael J. Thompson, and Linda J. Sauer Department of Chemistry, College of the How Cross Worcester, Massachusetts 0 16 10 Received August 16, 1982
Summary: Near-UV irradiation of Mn,(CO),L, (L = PBu, P(OEt),) in the presence of HCI and a variety of solvents yields both HMn(CO),L and Mn(CO),(L)CI. Evidence suggests the mechanism involves oxidative addition of HCI to 15- and 17-electron metal carbonyl radicals.
Evidence for the presence of metal carbonyl radicals (both neutral and ionic) in a variety of chemical reactions is growing rapidly.' By studying the chemistry of these radicals, a better understanding of probable chemical mechanisms is achieved. In addition to numerous CO substitution reactions,2 neutral manganese carbonyl radicals have been observed to react, by a variety of proposed mechanisms, with small molecules, including cc14,302,4 12,4Br2,5H2,6and HBrS7 In these reactions only single mononuclear produds were detected. In comparison, while looking at the reaction of Mn2(CO)A2(L = PBu,, P(OEt)3, and CO) with H20under acidic conditions, we observe that the reaction of HCl with photochemically generated Mn(CO)4Lradicals is unique in that it produces two carbon(1) (a) Nalesnik, T. E.; Orchin, M. Organometallics 1982,1,222-223. (b) Hershberger, J. W.; Klingler, R. J.; Kochi, J. K. J. Am. Chem. SOC. 1982, 104, 3034-3043. (c) Bruce, M. I.; Kehoe, D. C.; Matisons, J. G.; Nicholson, B. K.; Rieger, P. H.; Williams, M. L. J. Chem. SOC.,Chem. Commun. 1982,442-444. (d) Krusic, P. J.; San Filippo, J., Jr.; Hutch1981, 103, inson, B.; Hance, R. L.; Daniels, L. M. J. Am. Chem. SOC. 2129-2131. (2) McCullen, S. B.; Brown, T. L. Znorg. Chem. 1981,20, 3528-3533 and references therein. (3) Wrighton, M. S.; Ginley, D. S. J. Am. Chem. SOC. 1975, 97, 2065-2072. (4) (a) Haines, L. I. B.; Hopgood, D.; P&, A. J. J. Chem. SOC. A 1968, 421-428. (b) Jackson, R. A.; P d , A. Inorg. Chem. 1978,17,997-1003. (c) Kramer, G.; Patterson, J.; Po& A.; Ng, I,. Ibid. 1980, 19, 1161-1169. (5) (a) Hopgood, D. J. Ph.D. Thesis, London University, 1966. (b) Kramer, G.;Patterson, J. R.; Poi$ A. J. J. Chem. SOC.,Dalton Trans. 1979, 1165. (6) Byers, B. H.; Brown, T. L. J.Am. Chem. SOC. 1977,99,2527-2532. (7) Bamford, C. H.; Burley, J. W.; Coldbeck, M. J.Chem. SOC.,Dalton Trans. 1972, 1846-1852.
0276-7333f 83 f 23Q2-Q459$Q1.5Q fQ
459
yl-containing products, ~ i s - H M n ( c 0 ) ~and L cis-Mn(CO),(L)Cl. This report describes these HCl reactions under a variety of conditions and utilizes the appearance of two products for partial mechanism elucidation. Most of the solvent combinations employedsareflect the attempt to study the reaction of these water-insoluble compounds with water. The substituted carbonyls show only small solvent effects. When Mn2(C0)8L2(L = PBu, and P(OEt),) is dissolved in any of the solvent systems used" and irradiated,sb complete conversion of cis-HMn(CO)4Land cis-Mn(CO),(L)Cl is observed within about 30 min.g The rate of conversion shows some dependence on the HC1 concentraction. A small amount of hydrogen gas is also detected'O when the HC1 concentration is high. In contrast, Mn2(CO)loexhibits very marked solvent effects. Irradiation of Mn2(CO)loin the heterogeneous system (aqueous HCl/hexane) slowly produces HMn(CO&, Mn(CO),Cl, and some [Mn(CO),Cl],. After 24 h small amounts of hydrogen are also detected. However, irradiation of Mn2(CO)loin the homogeneous system (aqueous HCl/ethanol/isopropyl ether) causes only slow decomposition. When Mn2(CO)lois irradiated in the anhydrous HCl/hexane system, Mn(C0)&1 begins forming after 5 min. The concentration of Mn(CO)6C1increases for about 1h and then gradually converts to [Mn(CO),Cl],. There is no IR spectroscopic evidence for HMII(CO)~under these conditions even when high concentrations of Mn2(CO)lo are employed.'l This is consistent with the reported reaction between HBr and Mn2(CO)loin cyclohexane where only Mn(C0)6Br was d e t e ~ t e d . ~ When H2S04or HC2H302are employed in these photochemical reactions at concentrations comparable to those of HC1, HMII(CO)~L(L = PBu3, P(OEt),) forms but much more slowly than when HC1 is used. HN03 causes almost complete decomposition within 1 h. Photochemically generated radicals have been shown to be substitutionally labile: and there is significant evidence suggesting that facile dissociation of CO from these 17electron radicals is involved in substitution reactions.12 It follows that 15-electron radicals Mn(CO),L are also involved in these presently reported reactions with HC1. If so, running reactions under an atmosphere of CO should significantly decrease the concentration of these 15-electron radicals and, thereby, alter the reaction. Indeed, when these HC1 reactions are conducted under an atmosphere of CO, no hydride is formed and the rate of formation of chloride is reduced.', In light of these findings we propose (8) (a) Two sources of HC1 were examined. Homogeneous conditions were obtained in the following manner: gaseous hydrogen chloride was bubbled through hexane, isopropyl ether, or a 4% (by volume) ethanol/isopropyl ether mixture; aqueous hydrochloric acid was mixed with a 4% (by volume) ethanol/isopropyl ether mixture. Heterogeneous conditions (two phases) resulted when aqueous hydrochloric acid was stirred with hexane. (b) Typically, reaction solutions are prepared under a nitrogen atmosphere by using pure solvents stored over molecular sieves or alumina. The solutions are then purged for 15 min by using oxygenfree nitrogen (Linde) and kept under a positive pressure of nitrogen during irradiation. A 250-W mercury high intensity discharge lamp (GE H250A37-5) is used in conjunction with Pyrex filtering (A >300 nm). When a band-pass fiiter (Coming CS7-60 A- 352 nm with a band width at half-height of 60 nm) is employed, the reaction is slower (presumably due to the decrease in intensity), but the same products are formed. Samples for IR and GC analysis are taken via a serum cap and syringe. (9) Products are characterized by IR spectra: HMn(CO)4PBu3,YCO (cm-', isopropyl ether) 2057 (m), 1976 (m), 1960 (s), 1949 ( 8 ) ; Mn(CO),(PBu3)Cl,YCO (cm-', isopropyl ether) 2087 (m), 2018 (m), 2006 (a), 1948 (S).
(10)Hydrogen is detected by GC using Porapak Q packing. (11) Due to overlapping peaks, it is difficult to identify HMn(CO), spectroscopicallyuntil it is in high enough concentration so that the weak vibration at 2116 cm-l appears. (12) Wegman, R. W.; Olsen, R. J.; Gard, D. R.; Faulkner, L. R.; Brown, T. L. J. Am. Chem. SOC. 1981, 103, 6089-6092 and references therein.
0 1983 American Chemical Society
Organometallics 1983, 2, 460-462
460
A similar four-centered intermediate has been proposed for the oxidative addition of Hz or HzO to two CO(CN)~~-, Scheme I Also, disproportionation of metal 17-electron radi~a1s.I~~ carbonyl radicals in polar solvents is known.lg Mnz(CO)&z -!% ~MXI(CO)~L (1) Evidence supportive of a four-centered concerted process was sought by studying the photochemical reaction of MXI(CO)~L+ MII(CO)~L+ CO (2) aqueous HC1 with Mnz(CO)gPBu3dissolved in 4 % ethanol/isopropyl ether. On the basis of electronic effects, a Mn(C0)3L + HC1- HMII(CO)~LC~ (3) four-centered intermediate should favor formation of HMII(CO)~LC~ + MII(CO)~L HMII(CO)~and Mn(C0)4(PBu3)C1.If steric factors domHM~I(CO)~L + Mn(CO)3LC1 (4) inate, Mn(CO)&21 and HMn(C0)4PBu3 should form. Spectroscopic evidence indicates that only Mnz(CO)lo, MII(CO)~LC~ + CO MII(CO)~LC~ (5) HMn(C0)4PBu3,and Mn(C0)4(PBuJCl form in significant amounts within 20 min. This evidence strongly argues HMII(CO)~LC~ + HC1- Hz + Mn(C0)3LC1z (6) against a four-centered intermediate. Furthermore, irradiation of Mnz(CO)gPBu3in the absence of HC1 (4% Mn(CO)3LC1z+ MII(CO)~L ethanol/isopropyl ether) produces within 15 min a mixture MII(CO)~LC~ +Mn(CO),LCl (7) of Mnz(CO)loand Mnz(C0)8(PBu3)z in equilibrium with MII(CO)~LC~ + CO M ~ I ( C O ) ~ L C ~ (8) Mnz(CO)gPBu3. The appearance of these crossover products coupled with the lack of evidence for any anionic MII(CO)~L+ H C 1 7 MII(CO)~LC~ + HS (9) species, e.g., M~I(CO)~L-, indicate simple metal-metal bond homolysis is occurring without rapid disproportionation. Photochemical bond homolysis (eq 1) is followed by Lastly, it is interesting to briefly compare the thermal facile CO dissociation (eq 2). In step 3 HC1 undergoes a and photochemical reactions of Mnz(CO)8Lz(L = PBu3, two-electron oxidative addition to a coordinatively unP(OEt),, and CO) with HC1. In the absence of light, saturated lbelectron radical. Such a process is common thermal reactions (from 18 to 60 "C) of Mnz(CO)8Lzwith with HC1 and 16-electron species.15 It has also been HC1 show more pronounced ligand effects than the corproposed that oxidative addition of H t and HSn(r~-Bu)~l~ responding photochemical reactions. In all cases where to 15-electron metal carbonyl radicals occurs. The ligand reaction occurs, Mn(CO),(L)Cl always forms, whereas effect, associated with the increase in reaction rate obHMn(C0)4Lnever is detected. The reactivity of L is in served with the substituted compounds, further supports the order PBu3 > P(OEt), >> CO. Therefore, the ligand the oxidative addition pathway. The stronger Lewis bases effect is somewhat similar to that in the photochemical PBu3 and P(OEt)3(compared to the r acid CO) promote process, but the lack of formation of HMII(CO)~Lstrongly facile oxidation of the manganese. Hydrogen atom abindicates a different mechanism is operable. Further straction (eq 4) and CO addition (eq 5) complete the studies including kinetic measurements on both the process. When larger amounts of HC1 are present, a second thermal and photochemical reactions are in progress. HC1 molecule interacts evolving Hz gas (eq 6). Such a Acknowledgment. We are grateful for the William and process has also been proposed for reactions of HI with Flora Hewlett Foundation Grant of Research Corp. that Ir(1) species.l' Chlorine atom abstraction (eq 7) is then provided financial support for this research. followed by CO addition (eq 8). In step 9 one-electron oxidative addition (chloride abRegistry No. Mn2(C0)8(PBu3)2,15609-33-3; Mnz(CO)&P(OEt)3)2,1548&149; HCl, 7647-01-0; HMxI(CO)~PBU~, 56960-19-1; straction) is indicated. However, given the H-C1 bond HMn(C0)4P(OEt)3,84369-08-4;MxI(CO)~(PBU~)CI, 84369-09-5; strength (420 kJ/mol), the solvent would likely play a role. Mn(CO)4(P(OEt)3)Cl,84369-10-8; H2, 1333-74-0;CO, 630-08-0; Alternatively, an initial two-electron oxidative addition of Mn2(CO)lo, 10170-69-1; Mn(CO)5C1, 14100-30-2; HMn(CO)S, HC1 to MII(CO)~Loccurs (producing a seven-coordinate, 16972-33-1; M X I ~ ( C O ) ~ P 24476-71-9; BU~, hexane, 110-54-3; iso19-electronradical) followed by loss of H. There is growing propyl ether, 108-20-3; ethanol, 64-17-5. evidencela that 19-electron radicals are formed via associative processes, especially in disubstituted radicals.lsb (19)Allen, D.M.;Cox, A.; Kemp, T. J.; Sultana, Q.;Pitts, R. B. J. Step 9 predominates only when step 2 is supressed by an Chem. SOC.,Dalton Trans. 1976,1189-1193. atmosphere of CO. An alternative pathway involves the interaction of an HC1 molecule with a pair of solvent-caged radicals forming a four-centered intermediate. Such an interaction may be viewed either as a dinuclear, two-electron oxidative addition of HC1 or as an HC1-promoted disproportionation. Redox-Catalyzed Carbonylatlon of an Iron Methyl the mechanism shown in Scheme I.
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(13)When a small amount of oxygen (air) is added to the reaction of Mn2(CO)8L2and HCl, the gfowth of HMn(C0)L is inhibited. The observed effect of added CO is somewhat similar and may reflect trace amounts of O2in the CO. However, the CO (Linde, CP grade) is passed through an activated manganese(I1) oxide, oxygen-scavanging column" prior to use. Further testa are being conducted. (14)Brown, T. L.; Dickerhoof, D. W.; Bafw, D. A.; Morgan, G. L. Reu. Sci. Zmtrum. 1962,33,491-92. (15)(a) Louw, W.J.; deWaal, D. J. A.; Gerber, T. I. A.; Demanet, C. M.; Copperthwaite, R. G. Znorg. Chem. 1982,21,1667-68.(b) Halpern, J. Acc. Chem. Res. 1970,3,386-392 and references therein. (16)Wegman, R.W.;Brown, T. L. Organometallics 1982,1, 47-52. (17)Forster, D. J. Chem. SOC.,Dalton Trans. 1979,1639-1645. (18)(a) Fox, A.; Malito, J.; Po& A. J. Chem. SOC.,Chem. Commun. 1981,1052-1063.(b)McCullen, S.B.; Walker, H. W.; Brown, T. L. J.Am. Chem. SOC.1982,104,4007-4008.
0276-733318312302-0460$01.50/0
Complex Roy H. Magnuson,' Randy Melrowltr, Samu J. Zulu, and Warren P. Glerlng' Department of Chemistry, Boston University Boston, Massachusetts 022 15 Received October 25, 1982
Summaty: ($-C,H,)(PPh,)(CO)Fe(CH,) undergoes a rapid redox-catalyzed migratory insertion that follows the rate law: rate = k [OX],[CO]. 0 1983 American Chemical Society
