Organometallics 1995, 14, 5008-5010
5008
Reversible Insertion Reactions of a Platinum Germylene Complex Kyle E. Litz,? Kenneth Henderson, Randall W. Gourley,S and Mark M. Banaszak Holl*it Department of Chemistry, Brown University, Providence, Rhode Island 02912 Received August 16, 1995@ Summary: Dihydrogen and carbon dioxide react reversibly with the three-coordinate complex (Et3P)zPtGe[N(SiMed&. These reactions demonstrate the ability of germylenes to act as strong supporting ligands, while introducing new modes of reactivity via formal Ge(II)I Ge(N)interconversion. Despite the synthesis of many types of germylenes and metal-germylene complexes, the observed reactivity of metal germylene complexes has been dominated by irreversible insertion chemistry, resulting in the formal conversion of the germanium species from Ge(11) t o Ge(IV1.l The tendency of germylene ligands t o undergo insertion has limited their use as supporting ligands or as internal Lewis acids capable of enhancing transition-metal reactivity. We now wish to report the synthesis and crystal structure of the platinum germylene complex (Et3P)zPtGe[N(SiMe3)zIz(1) and the reversible reactions of 1 with dihydrogen and carbon dioxide, yielding cis-(Et3P)~Pt(H)GeH[N(SiMe3)zl~ (2) m
and cis-(Et3P)zPtC(O)Ge[N(SiMe3)~]~ (3), respectively. When a mixture of (Et3P)zPt(Cz04)(1.13g)2 and Ge[N(SiMe3)& (0.86 g)3was refluxed for 36 h in 50 mL of benzene under an argon atmosphere, the initially pale yellow solution turned a deep, intense yellow. All volatiles were removed in vacuo, and the resulting yellow powder was recrystallized from hexane, giving sparkling lemon yellow microcrystals of (Et3P)zPtGe[N(SiMe3)21z(1)(Scheme 114Integration of the IH NMR spectrum confirmed that the desired stoichiometry had been obtained, and an IR spectrum indicated that no oxalate fragments were present. Both 31P and lg5Pt NMR supported the assignment of a three-coordinate monomer, since no 3Jpt-p couplings indicative of a dimeric species were present. X-ray-quality crystals of 1 were obtained by slow evaporation of a 1:l benzene/ hexane solution. A single-crystal X-ray structure of 1 provided confirmation of the spectroscopic structure
* To whom correspondence should be addressed. E-mail: mbanasza@ umich.edu. + Current address: Chemistry Department, University of Michigan, Ann Arbor, MI 48109-1055. Current address: Fosroc, Inc., Georgetown, KY 40324. Abstract published in Advance ACS Abstracts, October 1, 1995. (1)For recent reviews see: (a) Neumann, W. P. Chem. Rev. 1991, 91, 311-334. (b) Barrau, J.; Escudi6, J.; Satg6, J. Chem. Rev. 1990, 90,283-319. (c) Lappert, M. F.; Rowe, R. S. Coord. Chem. Rev. 1990, 100.267-292. (d) Petz. W. Chem. Rev. 1986.86.1019-1047. (2) Paonessa, R. S.; Prignano, A. L.; Trogler, W.'C. Organometallics 1985,4, 647-657. (3)Gynane, M. J. S.; Harris, D. H.; Lappert, M. F.; Power, P. P.; Riviere, P.; Riviere-Baudet, M. J. Chem. Soc., Dalton Trans. 1977, 2004-2009. (4) Data for 1 are as follows: yield 64%; lH NMR (CsDe) 6 1.52 (4, 12H, 3 5 ~=- 7.7 ~ HZ, CHzCH&, 1.00 (t, 18H, 3 J ~ =- 7.7 ~ Hz, CH2CHdd, 0.51 (s, 36H, N(Si(CH&z); 13CNMR (CeDe)6 9.37 (pseudot, ~ J P - c= 10.4 Hz, CHZCHB),23.69 (m, IJP-C= 11.5 Hz, CHZCH3), 5.90 (s, Si(CH3)d; 31P{1H}NMR 6 38.3 (s with P t satellites, l J ~ - p= 4131 Hz); ls5Pt{lH} NMR 6 -4796 (t, V p t - p = 4130 Hz). The l e a p t and 31Pshifis are reported vs K2PtCls in DzO and 85% HaPo1 in DzO, respectively. Anal. Calcd for C~&&eN2P2PtSi4: C, 34.95; H, 8.07; N, 3.40. Found: C, 34.71; H, 8.06; N, 3.34. ~
assignment (Figure lh5 The geometry of the platinum and germanium atoms is trigonal planar with the P-Pt-P angle of 115.0(1)O somewhat smaller than the average P-Pt-Ge angle of 122.5(1)", consistent with steric effects. The orientation of the germylene ligand aligns the Ge pa orbital and the Pt dzy orbital for a n-bonding interaction. The observed Pt-Ge distance is 0.12-0.17 A shorter than the Pt-Ge bond length in the related complexes (Et3P)zPt(GeClMez)~,~ [(Pt{p-Ge[N(SiMe3)21~)(C0))31,~~ and (Et3P)zPt(H)GeH[N(Sie3)~12 (21, indicating that some Pt-Ge multiple bonding may
~
( 5 ) Crystal data for 1: a = 10.95512) A, b = 21.634(4) A, c = 16.319(4) A, /3 = 91.88(2)', V = 3865.5(14) A3, Z = 4, space group F'21/n, mol wt 824.77 for CzdH&eNzPzPtSid, density (calcd) 1.417 g/cm3, R = 0.051, R, = 0.115. Selected distances (A) and angles (deg): Pt-Ge, 2.304(1);PW-Pt, 2.263(3);P(2)-Pt, 2.261(3);N(l)-Ge, 1.874(7);N(2)Ge, 1.867(7); Si-N (av), 1.75(1);N(l)-Ge-N(2), 106.3(3);N(2)-GePt, 127.1(2); N(l)-Ge-Pt, 126.6(2); P(l)-Pt-P(2), 115.0(1); angle between P(l)-Pt-P(2) and N(l)-Ge-N(2) planes, 79.8(2).
0276-733319512314-5008$09.00/00 1995 American Chemical Society
Communications
Organometallics, Vol. 14, No. 11, 1995 5009
be o ~ c u r r i n g . ~However, *~ a similar decrease of about 0.1 A in the Pt-P bond length also occurs, suggesting that the change in Pt-Ge bond length is related to the change from four- to three-coordination. Competition from the two nitrogen bases attached to germanium may minimize platinum dry donation into the germanium pz 0rbita1.~ The observed orientation of the germylene ligand can be explained simply by steric effects. Exposure of a stirred benzene solution (15 mL) of 1 (0.490 g) t o 1 atm of H2 for 20 h at 20 "C results in a fading of the initially bright yellow solution t o a light tan color and the formation of cis-(Et3P)~Pt(H)Ge(H)[N(SiMe3)2]2(cis-2; Scheme 1). Off-white microcrystals were isolated via recrystallization from pentane.1° In principle, both platinum-centered oxidative addition followed by migratory insertion and 1,2-addition across the Pt-Ge bond are possible mechanisms for the formation of 2. However, during the synthesis a secondary compound is transiently present. We have assigned this product as trans-2, an intermediate which appears most consistent with an oxidative-additiodmigratory-insertion pathway.ll Three other pieces of information are worth noting. First, when cis-2 is heated for 12 h a t 80 "C under 3 atm of D2, complete conversion to cis-(EtgP)zPt(D)Ge(D)[N(SiMe3)212(d2-cis-2) occurs. Second, no incorporation of deuterium occurs over a 20-h time span a t 20 "C. Third, isomerization from transd to cis-2 takes less than 20 h at 20 "C. From these observations we can conclude that H D 2 exchange is slower than cistrans isomerization. Scheme 1illustrates the observed interconversions and an intermediate which we deem t o be most consistent with the experiments performed to date. A single crystal of 2 was grown from a saturated solution of a 1:l benzenehexane mixture, and
Figure 2. X-ray structure of cis-(Et3P)zPt(H)Ge(H)[N(TMS)21z(2). an X-ray structure determination was performed to extend the understanding of Pt-Ge bond lengths.lZ Distances and angles were largely unremarkable, with the exception of the Pt-Ge bond length. Unlike the analogous alkyl complexes, the cis conformation is not enforced by a bidentate ligand,13although steric effects certainly favor a cis complex. It is also interesting that cis-2 does not reductively eliminate upon heating, apparently preferring to follow an a-elimination pathway.14J5 The analogous complexes containing alkyls, cis-(R3P)zPtR(H),all undergo reductive elimination upon heating.13J6 The difference in reactivity probably stems from the relative C-H and Ge-H bond strengths (about 100 vs 70 kcal/mol, respectively) and the apparent strength of the Pt-Ge dative bond of 1. The observed reversibility allows the germylene ligand to function as a temporary %torage site" for a hydrogen atom. Although investigation of the Pt-Ge moiety of 1 with small molecules was a major goal of the research, we had initially ignored C02 as a potential substrate because 2 equiv of COZ is produced in the reaction forming 1. However, the reversible formation of 2 prompted us to pursue the reactivity of 1 with C 0 2 because the synthetic conditions employed could have prevented us from observing a reversibly formed complex. Exposure of a benzene solution of 1 to 1equiv of CO2 at 20 "C for 6 h resulted in the formation of cis-
(6) Yamashita, H.; Kobayashi, T.; Tanaka, M.; Samuels, J. A.; Streib, W. E. Organometallics 1992, 11, 2330-2333. (7) An analogous complex, (Ph3P)zPt[Ge(N(TMS)2)2], was previously described: Rowe, R. S. Ph.D. Thesis, University of Sussex, 1988.lCTo the best of our knowledge, a crystal structure has not been reported. Similar Pt(0) complexes have also been reported: (a)Hitchcock, P. B.; Lappert, M. L.; Misra, M. C. J . Chem. SOC.,Chem. Commun. 1985, 863-864. (b) Campbell, G. K.; Hitchcock, P. B.; Lappert, M. F.; Misra, M. C. J . Organomet. Chem. 1985,289, Cl-C4. (8)Few cases of M=Ge double bonds have been reported; examples include (a)GZide, W.; Weiss, E. J . Organomet. Chem. 1981,213,451460. (b) Herrmann, W. A.; Kneuper, H.-J.; Herdtweck, E. Chem. Ber. 1989, 122, 433-436. For theoretical discussion of the issue see: (c) Kostic, N. M.; Fenske, R. F. J . Organomet. Chem. 1982, 233, 337351. (Et3P)zPtC(O)OGe[(N(SiMe3)2]2 (3),17isolated as a white, (9)This has been observed in other systems, for example: (a) Herrmann, W. A.; Denk, M.; Behm, J.; Scherer, W.; Klingan, F.-R.; air-stable, microcrystalline solid by filtration from penBock, H.; Solouki, B.; Wagner, M. Angew. Chem., Int. Ed. Engl. 1992, tane (Scheme 1). The formation of a four-membered 31, 1485-1488. (b) Grumbine, S. D.; Tilley, T. D.; Arnold, F. P.; 1993, 115, 7884-7885. Rheingold, A. L. J . Am. Chem. SOC. 6 -4.54 (12) Crystal data for 2: a = 18.770(3)A, b = 12.376(2)A, c = 17.005(10) Data for cis-2 are as follows: yield 60%;'H NMR (dd with Pt satellites, 1 H, l J p t - ~= 847 Hz, VP-H= 22 Hz (trans), (2) A, p = 102.02(1)",V = 3863.6(10)A3, Z = 4, space group P21/c, mol V - H= 16 Hz (cis), 3 J H - H = 3.4 Hz, H-Pt), 6.95 (dd with Pt satellites, wt 826.78 for C24H6~GeNzP2PtSi4,density (calcd) 1.421 g/cm3, R = 1 H. 2 J m - ~= 167 Hz. ~JD-u = 9.7 Hz. 3 J ~=- 3.4 ~ Hz. H-Gel 1.64 0.094, R , = 0.22. Selected distances (A) and angles (deg): Pt-Ge, 2.422(2); P(l)-Pt, 2.285(4); P(2)-Pt, 2.300(4); N(l)-Ge, 1.91(1);N(2)(m,6H,'C&CH3), 1.46 (m, 6H, CHzCH,), 6:84 (m,18H,-CH2Cir3j, 0.59 Ge, 1.91(1); Si-N (av), 1.73(1); N(l)-Ge-N(2), 106.9(4); N(2)-Ge(s, 36H, N(Si(CHdd2; 13CNMR (CsD6) 6 8.51 (m, 2 J p - ~= 3.3 hz, 3 J p t - ~ Pt, 122.1(3);N(l)-Ge-Pt, 112.0(3); P(l)-Pt-P(2), 106.8(1);P(l)-Pt= 10.4 Hz, CHZCH~), 18.07 (m, ~JP-c = 24.9 Hz, VP-C = 3.0 Hz, 2 J p t - ~ = 22.6 Hz, CHZCH~), 21.75 (m, 4Jp-c = 25.0 Hz, 3 J p - ~= 2.9 Hz, 2 J ~ t - ~Ge, 159.0(1); P(B)-Pt-Ge, 92.7(1). (13)Similar structurally characterized compounds containing bi= 36.7 Hz. C H 4 H d . 6.30 (8. S i ( C H A : 31Pf1H\ NMR S 16.41 (d with dentate phosphines include: (a) Hackett, M.; Ibers, J. A.; Jernakoff, Pt satellites, z&-p = 14.98 Hz, l J p t - p = 2129 Hz), 9.31 ( V p - p = 15.06 Hz, l J ~ - p= 2112 Hz);lgsPt{lH} NMR 6 -5160 (pseudo-t, apparent P.; Whitesides, G. M. J . Am. Chem. SOC.1986, 108, 8094-8095. (b) Hackett, M.; Ibers, J. A.; Whitesides, G. M. J . Am. Chem. SOC.1988, V p t - p = 2124 Hz). IR (Nujol mull, cm-l): modes a t 2115 (m) and 1949 (m),probably the Ge-H and Pt-H stretches, respectively, are observed 110, 1436-1448. (c) Mullica, D. F.; Sappenfield, E. L.; HampdenSmith, M. J. Polyhedron 1991, 10, 867-872. to shift as expected upon deuterium labeling. We have not been able (14) We cannot rule out a 1,2-elimination of dihydrogen. Another to unambiguously assign which stretch is associated with which moiety. example of a proposed a-elimination: Yamashita, H.; Kobayashi, T.; Anal. Calcd for C2&&eN2P2PtSi4: C, 34.86; H, 8.29; N, 3.39. Tanaka, M.; Samuels, J. A.; Streib, W. E. Organometallics 1992, 11, Found: C, 34.71; H, 8.20; N, 3.22. (11)Data for trans-2 are as follows: lH NMR (C6D12) S -8.00 (td 2330-2333. (15) 1,2-Eliminations have been reported for base-stabilized si= 796 Hz, = 19 Hz (cis), 35H-H = with Pt satellites, 1H, ~JR-H lylenes: Chauhan, B. P. S.; Corriu, R. J . p.; Lanneau, G. F.; Priou, c.; 7.8 Hz, H-Pt), 7.21 (m with Pt satellites, 1H, Vpt-~= 159 Hz, H-Gel. Auner, N.; Handwerker, H.; Herdtweck, E. Organometallics 1995,14, The Et3P and N(TMS)2 groups overlap with the shifts for cis-2. Comparative shifts for cis-2 in C6D12 are 6 -4.53 and 6.67 for Pt-H 1657-1666. and Ge-H, respectively. The Ge-H resonance for trans-2 is partially (16) Hackett, M.; Whitesides, G. M. J . Am. Chem. SOC. 1988, 110, 1449-1462. obscured by solvent in C ~ D G .
-
~~~
~
5010 Organometallics, Vol. 14,No.11, 1995
Figure 3. X-ray structure of cis-(Et3P)zPtC(O)OGe[N(TMS)zlz(3).
metallacycle was suggested by the observation of two new bands in the IR at 1622 and 1091 cm-l, 'H, 31P, and lg5PtNMR spectra consistent with a square-planar complex, and the observation of the COz-derived signal in the 13C NMR spectrum at 171.35 ppm (lJpt-c = 891 Hz). The IR and 13CNMR data are consistent with the four previously characterized examples of C02 moieties side-bound t o a metal and a heteroatom.la However, these previous examples were generated by alkoxide attack on bound CO ligands, not by direct reaction with free C02. X-ray-quality crystals were grown by cooling a toluene solution under a C 0 2 atmosphere, and the structure was determined to confirm the spectroscopic assignment.lg As shown in Figure 3, complex 3 has a COS molecule side-bound t o the Pt-Ge moiety. The four-membered metallacycle is highly distorted as a consequence of the greatly differing Pt-Ge (2.420A) and C - 0 (1.33 A) bond lengths. In addition, the ring is puckered such that the C02 fragment makes an angle of 15' with respect to the Pt-Ge bond vector. All previous examples of this binding mode exhibited planar rings. l8 Metallacycle distortion also affects the geometry about the nominally square-planar platinum center, (17) Data for 3 are as follows: yield 70%; 'H NMR (CsDs) d 0.81 (m, 18 H, CHZCH~), 1.61 (m, 6 H, CHZCH~), 1.86 (m, 6 H, CHZCH~), 9.15 (m, 0.59 (s, 36 H, Si(CH&); 13C NMR (C&) d 8.41 (m, CHZCH~), CHZCH~), 15.99 (m, IJp-c = 27.2 Hz, CHZCH~), 21.01 (m, ~JP-c = 24.4 Hz, CHZCH~), 7.06 (s, Si(CH3)3),171.35 (dd with Pt satellites, Vp-c = 131 Hz (trans), Vp-c = 4 Hz (cis), lJpt-c = 891 Hz); 31P{1H}NMR d 3.83 (d with Pt satellites, 2 J p - p = 11.5 Hz, l J p t - p = 1758 Hz), 20.95 (d with Pt satellites, V p - p = 11.5Hz, lJpt-p = 2380 Hz); 19sPt{1H}NMR 6 -4363 (dd, l J p t - p = 1757 and 2387 Hz); IR (Nujol mull, cm-') 1622 (C=O), 1091 (C-0). These bands shifted to 1585 and 1069 cm-l, respectively, upon 13Clabeling, consistent with the harmonic oscillator approximation. An excess of COz is best for making 3 in quantity. (18)(a) Wegner, P. A.; Guggenburger, L. J.; Muetterties, E. L. J. Am. Chem. SOC. 1970,92,3473-3474. (b) Vaughn, G. D.; Strouse, C. E.; Gladysz, J. A. J . Am. Chem. SOC. 1986,108, 1462-1473. (c) Field, J. S.;Haines, R. J.; Sundermeyer, J.;Woollam, F. J.Chem. Soc., Chem. Commun. 1990,985-988. (d) Field, J. S.; Haines, R. J.; Sundermeyer, J.;Woollam, F. J . Chem. SOC.,Dalton Trans. 1993,2735-2748. Other related complexes include: (e) Bennett, M. A.; Jin, H.; Willis, A. C. J. Organomet. Chem. 1993, 451, 249-256. (f)Szalda, D. J.; Chou, M. H.; Fujita, E.; Creutz, C. Inorg. Chem. 1992, 31, 4712-4714. (19) Crystal data for 3: a = 15.520(2)A, b = 13.618(2)A, c = 37.156(6) A, V = 7853(2) A3, Z = 8, space group Pbca, mol wt 868.78 for C Z S H S S G ~ N ~ ~ Z density P Z P ~ S(calcd) ~ ~ , 1.470 g/cm3, R = 0.052, R, = 0.096. Selected distances (A) and angles (deg): Pt-Ge, 2.4197(9);PtC(251, 2.086(9); C(25)-0(1), 1.333(10);C(25)-0(2), 1.214(10);P(1)Pt, 2.309(2);P(2)-Pt, 2.346(2);N(l)-Ge, 1.864(6);N(2)-Ge, 1.882(7); Si-N (av), 1.748(1);P(l)-Pt-P(2), 98.97(8); P(B)-Pt-Ge, 105.92(6); P(l)-Pt-C(25), 89.1(2); C(25)-Pt-Ge, 65.8; P(l)-Pt-Ge, 154.87(6); P(2)-Pt-C(25), 167.0(3);Pt-C(25)-0(1), 110.5(6); C(25)-0(1)-Ge(11, 98.5(5); O(1)-Ge-Pt, 81.7(2); O(l)-C(25)-0(2), 119.9(9);O(2)C(25)-Pt, 129.4(7); N(l)-Ge-O(l), 105.4(3); N(2)-Ge-O(1), 98.3; N(l)-Ge-N(2), 110.0(3);N(B)-Ge-Pt, 123.4(2);N(l)-Ge-Pt, 124.6(2).
Communications reducing the C(25FPt-Ge angle to 65.8'. Despite or perhaps because of the considerable distortion of the metallacycle and the platinum center, all bond lengths fall within expected limits. Coordination about the germanium atom, also affected by the metallacycleinduced distortions, is best described as a distorted trigonal pyramid, the base formed by the platinum, germanium, and nitrogen atoms with O(1) forming the cap.20 Previous examples of inserted germylene complexes have been better described as tetrahedral.21122 As expected on the basis of the fact that we do not isolate 3 from the reaction used to form 1,heating 3 to 80 "C causes the clear, colorless solution to turn yellow, regenerating 1 and producing C02. In a sealed tube containing 1 equiv of COz, the mixture can be cycled between 1 and 3 by heating t o form 1 and cooling the tube, re-forming 3. Although 3 is an air-stable compound, hydrocarbon solutions of 3 slowly decompose by giving off C02 and re-forming air-sensitive 1, which is oxidized. The presence of the germylene ligand and the formation of a Ge-0 bond is clearly crucial for the reaction of 1 with C02, differentiating 1 from other three-coordinate Pt(0) complexes containing dative, twoelectron donors. The similar three-coordinate complex Pt(PPhd3 does not react with C02.23 Despite the apparent analogy to metal carbene chemistry shown in the formation of metallacycle 3,alkenes such as ethylene and norbornene do not react with 1 to form a metallacyclobutane. In conclusion, the new germylene complexes cis(Et3P)aPt(H)Ge(H)[N(SiMe3)232 (cis-2) and cis-(Et3P)zm
PtC(O)OGe[N(SiMe3)212(3)have been synthesized from the common precursor (EtsP)zPtGe[N(SiMe3)212(1). The clean, reversible nature of the reactions observed is a unique observation in germylene insertion chemistry, which highlights the ability of germylenes t o function as "supporting" ligands while also facilitating new types of reactivity. Acknowledgment. The donors of the Petroleum Research Fund, administered by the ACS, are thanked for support of this research (Grant No. 26966-G3). The X-ray equipment was purchased with assistance from grants from the National Science Foundation (Grant No. CHE-8206423) and the National Institutes of Health (Grant No. RR-06462). D. A. Sweigart and P. T. Wolczanski are thanked for valuable discussions. Supporting Information Available: Further details concerning the X-ray crystal structures of complexes 1-3, including tables of crystal data and structure refinement details,positional and thermal parameters,and bond distances and angles (19 pages). This material is contained in many libraries on microfiche, immediately follows this article in the microfilm version of this journal, can be ordered from the ACS, and can be downloaded from the Internet; see any current
masthead page for ordering information and Internet access instructions.
OM950649Q (20) The mean deviation from a plane for Pt, Ge, N(1), and N(2) is just 0.061 A. (21) Examples include: (a) Veith, M.; Stahl, L.; Huch, V. Organometallics 1993,12, 1914-1920. (b) Hawkins, S. M.; Hitchcock, P. B.; Lappert, M. F.; Rai, A. K. J. Chem. Soc., Chem. Commun. 1986,16891690. (22) Trigonal-pyramidal complexes of germanium are known: (a) Gurkova, S. N.; Gusev, A. I.; Alexeev, N. V.; Segelman, R. I.; Gar, T. K.; Khromova, N. Yu.Zh. Strukt. Khim. 1983,24, 162. (b) Gurkova, S. N.; Gusev, A. I.; Alexeev, N. V.; Segelman, R. I.; Gar, T. K.; Khromova. N. Yu.Zh. Strukt. Khim. 1983.24. 83-85. (23)Nyman, C. J.; Wymore, C . E.; Wilkinson, G. J . Chem. SOC.A 1968, 561-563.
