Metal clusters. 21. Synthesis of rhodium phosphite clusters

Sivak, Andrew; Muetterties, E. L.

doi:10.1021/ja00511a016

Cited by 96 publications

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References 5 publications

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“…Representation of the catalytic cycle for the olefin hydrogenation cycle catalyzed by H2Rh2(P(O~i~C3H7)3]4 [31].…”

Section: ~mentioning

confidence: 99%

Cluster Chemistry

Muetterties

1980

Journal of Organometallic Chemistry

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whose fine structural details were not resolved until much later because of 1 2 exploded in the sixties and seventies through the efforts of many and especially those of the research groups of Chini, Lewis and Johnson; and Dahl. Size of these carbonyl clusters now has the impressive range of from to thirty~eight, the latter probably a number that has been exceeded or will soon be exceeded by the time this article is in print. A representative list of carbonyl clusters is given in Table II I see the most funda~ental differences between clusters and surfaces in the context of the coordination features of the peripheral urface) metal atoms [8]. The metal-metal coordination number of the peripheral metal atoms in molecular clusters ranges from two in 3-atom clusters to four in octahedral clusters to six in Pt3a(C0)~~2~ whereas the coordination number for flat metal surfaces is typically in the range of nine to six although it is as low as four for the (100) face of a body-centered cubic metal structure [8]. Metal~ligand coordination numbers for peripheral metal atoms in clusters are typically much larger than for the surface atoms in metals on which chemisorbed molecules or molecular fragments are presentThe metal-ligand coordination numbers are four in Os3(C0)12, three in sharp contrast to the surface metal-ligand coordination numbers which generally are less than one. Obviously, the disparity in values for these two types of coordination numbers decreases as molecular cluster size increases and metal particle size decreases and the crude analogy should be more useful for the large cluster-small metal particle comparisons. The features of the largest structurally established [14] molecular cluster~ Pt 38 (C0)~~2 -, nicely illustrate this point since this cluster has cubooctahedral form with exposed faces of (111) and (100) or ethyl, the nuclearity 1 n, is three and with R isopropyl, the nuclearity is two. All essentially have 16--electron square metal coordination sites. The d:Lmer consists of an essentially set of rhodium, hydrogen and phosphorus atoms (Figure 3). An edge~bridged set of three square planar Rh coordination spheres is :fotmd in the trimer as show"TI in Figure 4 for the crystallographically established {HRh [P (OG1 3 ) 3 ]z h complex.The chemistry of these rhodium hydrides is rather surprising. polynuclear hydrides to form not mononuclear H 3 Rh[P(OR) 3 ] 2 complexes but polynuclear rhodium polyhydrides~ equations (3) and (4).Nuclear magnetic resonance studies of these polynuclear polyhydrides have established for the dimer the tris(hydrido) bridged dimer structure illustrated in Figure 5.Both the trimeric and dimeric rhodium hydrides are very active olefin hydrogenation catalysts. Turnover rates at 20°C are between 1 and 100 per second. Reaction of the complexes with olefins is slow and complex whereas the reaction with hydrogen as noted above is virtually instantaneous.Hence the polyhydride is the first key intermediate in the catalytic cycle fluxional structure, and a key intermediate form im...

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“…Representation of the catalytic cycle for the olefin hydrogenation cycle catalyzed by H2Rh2(P(O~i~C3H7)3]4 [31].…”

Section: ~mentioning

confidence: 99%

Cluster Chemistry

Muetterties

1980

Journal of Organometallic Chemistry

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“…Dimer and trimer molecules each added precisely one molecule of hydrogen to form H4Rh2[P(O-i-C3H7)3]4 and H5Rh3[P(OCH3)3]6, respectively. On the basis of the 'H and 'Hf31PJ NMR spectra, the former is proposed to have a triple hydrogen bridged structure of the form p Hb wherein the bonding interaction is solely based on Rh-H-Rh three-center bonds; there is no net, direct Rh-Rh bonding (10). Effectively, the hydrogen addition to the dimer occurs over one Rh center although one Rh-H-Rh bridge bond is formed.…”

Section: Resultsmentioning

confidence: 99%

“…Thus, this putative cluster model of ethylene hydrogenation at a metal surface comprises hydrogen addition largely at one metal center and initial olefin complexation at an adjacent metal center. On a metal surface, the high mobility of Angles Rh1-H1l = 1.838 (10) Rh1-H2 = 1.734(11) Rh2-H2 = 1.732 (11) Rh2-H:j = 1.753(13) Rh3-H, = 1.750 (12) Rh3-H3 = 1.785 (12) Rh1-Rh2-Rh3 = 58.8(2) Rh2-Rh3-Rh1 = 59.6 (2) Rh3-Rh1-Rh2 = 61.5 (2) HI-Rhl H2 = 91.9 (5) H2-Rh2-H3 = 92.5 (6) HI-Rh3-H3 = 90.8 (6) P1-Rhl-P2 = 91.3 (3) P3-Rh2-P4 = 93.9(3) P5-Rh3-P6 = 94.9 (3) HI-Rhi-P, = 171.7 (4) H1-Rhl-P2 = 94.2(4) H2-Rhl-P, = 80.9 (4) …”

Section: Resultsmentioning

confidence: 99%

“…This complex was prepared by hydrogenolysis of '3-C3H5Rh[P(O-i-C3H7)3j2 at 20'C and with hydrogen at 1 atm (101.3 kilopascals) (9)(10)(11). Single crystals of the dimer were obtained by slow cooling, to -30'C, of pentane solutions of the hydride.…”

Section: Methodsmentioning

confidence: 99%

“…By using coordinately unsaturated metal clusters, the probability of cluster fragmentation in reactions can be substantially decreased. We describe here the structural features of a set of coordinately unsaturated polynuclear rhodium hydrides that exhibit high catalytic activity (9,10) in olefin hydrogenation reactions and that do not significantly fragment in these catalytic reactions.…”

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