J. Am. Chem. SOC. 1981, 103, 1278-1279
1278
Stepwise Reduction of CO to CH4 on a Triosmium Cluster Face. Preparation and Characterization of
os3(co)1lCH2
Guy R. Steinmetz and Gregory L. Geoffrey* Department of Chemistry, The Pennsylvania State University University Park, Pennsylvania 16802 Received October 20, 1980 Numerous mechanistic schemes have been proposed for the metal-surface-catalyzed reduction of CO to yield Many of these invoke formyl intermediates with reaction sequences similar to that outlined below for the hydrogenation of CO to CH41-3 We have been attempting to assess the feasibility of such 0
OH
Ill
"C//"M
H-C-M
I
It
I
M-
3
2
1
H H-C-M
I
I/ \M M-
193 CH4
4
transformations by using metal cluster complexes to model the proposed surface intermediates. Our initial focus has been on studies of the preparation and reactivity of formyl substituted clusters as models for 2. Herein we describe the reaction of [ O S ~ ( C O ) ~ ~ ( C H Owith ) ] - acid which yields the new methylene cluster O S ~ ( C O ) ~ ~ aCmimic H ~ , for the surface intermediate 4. The latter cluster when heated under an H2 atmosphere evolves CH4, and thus the stepwise reduction of CO to CH4 on an Os3 cluster face is demonstrated. Treatment of O S ~ ( C Oin) ~tetrahydrofuran ~ (THF) with K[ B H ( O - ~ - P Y )at~ ]O O C gives an intense orange solution which shows an IR band at 1577 cm-' and a singlet at 6 16.0 in its 'H N M R spectrum. These spectral data indicate the presence of a formyl substituent and suggest the formation of [OS~(CO)~,(CH0)]-. Upon warmup to 25 OC, the solution turns dark orange and the IR band at 1577 cm-' decreases in intensity as a new band at 1710 cm-l grows in. This transformation is complete within -2.5 h. At this point metathesis with [(Ph3P)2N]C1leads to the isolation of [(Ph3P),N] [ H O S ~ ( C O ) ~which ~ ] , ~apparently derives from the formyl complex by the deinsertion reaction shown in eq 1. Similar results have been obtained by Pruett and ceworkers' O S ~ ( C O+) ~[BH(O-i-Pr)3]~ [OS~(CO)~~(CHO)]-
-
[HOs3(CO)iil- (1) who treated T H F solutions of O S ~ ( C Owith ) ~ ~Li[BHEt31. In an attempt to isolate a stable neutral product, excess 20% H3P04was added to the [OS~(CO)~~(CHO)]solution when this species' 1577 cm-I IR band was at its maximum intensity (-45 min at 0 O C after addition of K[BH(O-i-Pr)3]). The solution immediately turned dark red and workup by preparative scale liquid chromatography on silica with hexane eluant gave an orange-red, air-stable solid in typical yields of 20-30%. This material analysis and by its was identified as O S ~ ( C O ) ~ ~byCchemical H~ ~
~
~~
~
~
~~~
(1) Huang, C. P.; Richardson, J. T. J . Card. 1978, 51, 1. (2) Pichler, H.; Schultz, H. Chem. Zng. Tech. 1970, 42, 1162. (3) Henrici-Olivb, G.; Olive, S.Angew. Chem., Znt. Ed. Engl. 1976, 15, 136. (4) Araki, M.; Ponec, V. J . Caral. 1976, 44, 439. (5) van Barneveld, W. A. A,; Ponec, V. J. Carol. 1978, 51, 426. (6) Addition of [(Ph3P)2N]Clfollowed by hexane to a THF solution of the Os3(CO)lz/K[BH(O-i-Pr)3] reaction mixture held at -30 OC gave [(PhAzN][HOs3(CO),,] as a microcrystalline yellow-oran e powder in 72%
yield. The compound was identified by comparison of its fH NMR and IR spectra to those reported by: Eady, C. R.; Johnson, B. F. G.; Lewis, J.; Malatesta, M. C. J. Chem. SOC.,Dalron Trans. 1978, 1358. (7) Pruett, R. L.; Schoening, R. C.; Vidal, J. L.;Fiato, R. A. J. Orgammer. Chem. 1979, 182, C57.
0002-7863/81/1503-1278%01.25/0
165
160gppmlf5
If0
---t-62 5
Figure 1. 13CN M R spectra of Os3(CO)IICHzin CD2C12: (a) fully 'H coupled, (b) I3C{lHa},and (c) 13C('HbJ.J'3C-H, = 144 H z and JI3C-Hb = 147 Hz. Resonances at 171 and 183 ppm marked with an * are due to O S ~ ( C O impurity. )~~
I
I
z7 5
6.4 7
Figure 2. ' H NMR spectrum of O S ~ ( C O ) ~ ~inC CDCI3 H ~ solution. Scheme I OSg(C0)lp
+
[BHR3]
-
-
[OS~(CO)~,(CHO)]
-
H*
[OS~(CO)~~(=CHOH)] [ O S ~ ( C O I I ~ ( C H O-) I [Os3(COIlI(CH20H
)I- +
Os,(CO),2
IH+ H$
+
Os3(CO),,CHp
spectral properties: mass spectrum, m/e 894 (parent), fragment ions corresponding to loss of 11 CO's and 2 H's; IR (hexane solution) 2116 w, 2063 s, 2031 s, 2010 m, 1995 m, 1920 vw,1869 vw ~ m - ' . ~Anal. , ~ Calcd: C, 15.92; H , 0.45. Found: C, 16.14; H , 0.23. A I3C enriched sample of O S ~ ( C O ) ~ ~was C Hprepared ~ by treating "CO enriched oS3(CO)12 with K[BH(O-i-Pr),] followed by H3P04acidification. The 13CN M R spectrum of this material is shown in Figure la. The seven resonances in the 171-193-ppm (8) O S ~ ( C O ) ~ ~differs C H ~from the previously reported Hz0s3(CO)loCHz (Calvert, R. B.; Shapley, J. R. J . Am. Chem. SOC.1977,99,5225, corrected in Zbid. 1978,100,6544) by substitution of a carbonyl for two hydrides. For comparison, H ~ O S ~ ( C O ) ~shows ~ C H'H~ NMR resonances at 6 4.32, 5.12, 15.38, and 20.71. (9) Os3(CO),lCHz has also been recently prepared by J. R. Shapley and -workers by the addition of CHzN2to Os3(CO)lI(CH3CN). (J. R. Shapley, personal communication.)
0 1981 American Chemical Societv
J. Am. Chem. SOC.1981,103, 1279-1281
1279
Note that according to this mechanism, both methylene hydrogens derive from the [BHR3]- reducing agent, via the intermediacy of [OS~(CO)~~(CHO)]-, in accord with the experimental observations. When O S ~ ( C O ) ~ ~was C Hheated ~ to 70-80 OC under an H2 atmosphere, CH4 was evolved in -20% yield, as evidenced by n mass spectral analysis of the gases above such solution^.^^ Only CH2D2was produced when O S ~ ( C O ) ~ , Cwas H ~heated under a D2 atmosphere. The only Os-containing products from these reactions which could be identified were small amounts of Os3(CO)12(
