796 Organometallics 1995, 14, 796-803 Structural and Reactivity Consequences of the Presence of Lone Pairs in Main-Group-Transition-MetalCluster Compounds: Conversion of [HAs{Fe(C0)4}3l2- into [Fe3(CO)9(~3-ksFe(CO)4}212- Robert E. Bachman, Suzanne K. Miller, and Kenton H. Whitmire" Department of Chemistry, Rice University, P.O. Box 1892, Houston, Texas 77251 Received June 24, 1994@ The reaction of NaAsO2 with Fe(C0)dKOWMeOH produces the novel hydrido cluster [HA~(Fe(C0)4}31~-. An X-ray structural study was carried out on the [PPNl+ salt at 173 K in an attempt to crystallographically confirm the presence of the hydrogen atom. The material crystallizes in the trigonal space group P3 (No. 147) with a = 25.379(4) A, b = 25.379(4) A, c = 22.442(4) A, V = 12518.2(36) A3, and 2 = 6. The reactivity of this unusual cluster anion was probed by pyrolysis, photolysis, and protonation. Addition of acid produced the previously characterized cluster AszFes(CO)22. Pyrolysis and thermolysis both yielded the dianion [F~~(CO)~{,P~-ASF~(CO)~}~]~-. This material was crystallized as its [Et4Nl+ salt, and the structure was determined by single-crystal X-ray diffraction. [E~$JI~[AS~F~~(CO)I~I crystallizes in the triclinic space group Pi (No. 2) with a = 12.466(2) A, b = 13.408(3) A, c = 15.457(3) A, a = 80.59(3)", p = 72.01(3)", y = 66.66(3)", and V = 2253.7(8) A3. The cluster consists of a distorted-square-pyramidal E2M3 core with the two main-group atoms ligated by Fe(C0)4 fragments. Comparisons of the structure and reactivity of both [PPNl2[HAs- {Fe(C0)4}31 and [Et4Nl~[Fe~(CO)~{~~-AsFe(C0)~}~l with those of other isoelectronic and isostructural clusters containing either group 15 or 16 elements has led to a correlation between the observed structure and reactivity patterns and the presence of a lone pair of electrons on the main-group element. Introduction Transition-metal clusters which contain main-group fragments have been of interest for many years due to their unusual bonding and reactivity patterns.l The first arsenic-containing transition-metal clusters were prepared in the late 1950s by Hieber and co-workers from the reaction of arsenic oxides with Fe(C0)5in basic methanol followed by acidification.2 However, the initially formed anionic species from this reaction were not characterized due to limitations in the analytic tools available at the time. Since arsenic lies at the midpoint of the group 15 elements, its study should provide important information about structural and reactivity trends as the main-group element increases in size and in metallic character. This intermediate behavior has been demonstrated by clusters such as Fe3(CO)g- ASP^)^,^ which has an isostructural counterpart in the analogous, lighter P-containing compound, and As2- {W(C0)5}3, which which is similar to compounds con- taining heavier antimony and bismuth atoms.4 @ Abstract published in Advance ACS Abstracts, December 15,1994. (1) For recent reviews see: (a) Scherer, 0. J. Angew. Chem., Int. Ed. Engl. 1985,24,924. (b) Herrmann, W. A. Angew. Chem., Int. Ed, Engl. 1986, 25,56. (c) Huttner, G. Pure Appl. Chem. 1986, 58, 585. (d) Whitmire, K. H. J. Coord. Chem. B 1988,17,95. (e) Fenske, D.; Ohmer, J.; Hachgenei, J.; Merzweiler, K. Angew. Chem., Int. Ed. Engl. l988,27, 1277. (0 Norman, N. C. Chem. SOC. Rev. 1988, 17,269. (g) Scherer, 0. J. Angew. Chem., Int. Ed. Engl. 1990,29, 1104. (h) Compton, N. A.; Errington, R. J.; Norman, N. C. Adu. Organomet. Chem. 1990,31,91. (i) Whitmire, K. H. J. Cluster Sci. 1991,2,231. (j) Roof, L. C.; Kolis, J. W. Chem. Rev. 1993,93,1037. (2) Hieber, W.; Gruber, J.; Lux, F. Z. Anorg. Allg. Chem. 1959,300, 275. (3) Huttner, G.; Mohr, G.; Frank, A,; Schubert, U. J. Organomet. Chem. 1976.118. C73. (4) Sigwakh, B.; Zsolnai, L.; Berke, H.; Huttner, G. J. Organomet. Chem. 1982,226, C5. We recently reported the synthesis and structural characterization of the novel anionic species [HAS- {Fe(C0)4)3l2- ([I12-).5 In the study of the reactivity of this unusual species and the related clusters [E{Fe- (C0)4)3l2- (E = Se, Te),6 it has become apparent that their reactivities are distinctly different even though they are essentially isostructural and isoelectronic. The major feature which distinguishes these sets of clusters is the presence or absence of a lone pair on the main- group element. This paper explores the effect that the presence or absence of these lone pairs has on both the structure and reactivity of several isoelectronic and isostructural clusters which contain group 15 and 16 elements. Experimental Procedures General Considerations. All reactions and other ma- nipulations were performed with oven-dried Schlenkware using standard techniques on a Schlenk line or in a Vacuum Atmospheres drybox. All solvents were dried and distilled under nitrogen prior to use: methanol (Mg),THF (NaPhzCO), and hexane (LiAlH4). Bis(triphenylphosphine)nitrogen(l+) chloride, [PPNICl, was prepared according to literature meth- od~.~ Fe(C0)b (Aldrich), NaAsOz (Baker), [EtSIBr (Janssen), and KOH (EM Science) were used as received without further purification. Solution IR spectra were recorded in 0.1 mm pathlength CaF2 cells on a Perkin-Elmer Model 1640 FT-IR spectrophotometer. IH and 13C NMR spectra were obtained on a Bruker A?$ 300 spectrometer in THF-da. EI, FAB, and (5) Bachman, R. E.; Miller, S. IC; Whitmire, K. H. Inorg. Chem. (6) Bachman, R. E.; Whitmire, K. H. Inorg. Chem., in press. (7) Ruff, J. K.; Schlientz, W. S. Inorg. Synth. 1975, 15, 84. 1994,33, 2075. 0276-7333/95/2314-0796$09.00/0 0 1995 American Chemical Society