PROFILPELAJAR.COM

Tris(triphenylphosphine)rhodium carbonyl hydride
Identifiers
CAS Number	17185-29-4 ;
3D model (JSmol)	Interactive image;
ECHA InfoCard	100.037.467
EC Number	241-230-3;
UNII	720P7594ZM ;
CompTox Dashboard (EPA)	DTXSID40904295 ;
	InChI InChI=1S/3C18H15P.CO.Rh.H/c31-4-10-16(11-5-1)19(17-12-6-2-7-13-17)18-14-8-3-9-15-18;1-2;;/h31-15H;;; Key: AACIZACVKFEETJ-UHFFFAOYSA-N;
	SMILES [C-]#[O+].C1=CC=C(C=C1)P(C2=CC=CC=C2)C3=CC=CC=C3.C1=CC=C(C=C1)P(C2=CC=CC=C2)C3=CC=CC=C3.C1=CC=C(C=C1)P(C2=CC=CC=C2)C3=CC=CC=C3.[RhH];
Properties
Chemical formula	C55H46OP3Rh
Molar mass	918.78
Appearance	yellow solid
Melting point	172–174 °C (342–345 °F; 445–447 K) sealed capillary
Hazards
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H301, H311, H315, H319, H331, H335
Precautionary statements	P261, P264, P270, P271, P280, P301+P310, P302+P352, P304+P340, P305+P351+P338, P311, P312, P321, P322, P330, P332+P313, P337+P313, P361, P362, P363, P403+P233, P405, P501
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Carbonyl hydrido tris(triphenylphosphine)rhodium(I) [Carbonyl(hydrido)tris(triphenylphosphane)rhodium(I)] is an organorhodium compound with the formula [RhH(CO)(PPh₃)₃] (Ph = C₆H₅). It is a yellow, benzene-soluble solid, which is used industrially for hydroformylation.^[1]

Preparation

[RhH(CO)(PPh₃)₃] was first prepared by the reduction of [RhCl(CO)(PPh₃)₂], e.g. with sodium tetrahydroborate, or triethylamine and hydrogen, in ethanol in the presence of excess triphenylphosphine:

[RhCl(CO)(PPh₃)₂] + NaBH₄ + PPh₃ → [RhH(CO)(PPh₃)₃] + NaCl + BH₃

It can also be prepared from an aldehyde, rhodium trichloride and triphenylphosphine in basic alcoholic media.^[2]

Structure

The complex adopts a trigonal bipyramidal geometry with trans CO and hydrido ligands, resulting in pseudo-C_3v symmetry. The Rh-P, Rh-C, and Rh-H distances are 2.32, 1.83, and 1.60 Å, respectively.^[3]^[4] This complex is one of a small number of stable pentacoordinate rhodium hydrides.

Use in hydroformylation

This precatalyst was uncovered in attempts to use tris(triphenylphosphine)rhodium chloride as a hydroformylation catalyst. It was found that the complex would quickly carbonylate and that the catalytic activity of the resulting material was enhanced by a variety of additives but inhibited by halides. This inhibition did not occur in the presence of base, suggesting that the hydrido-complex represented the catalytic form of the complex.^[5]

Mechanistic considerations

[RhH(CO)(PPh₃)₃] is a catalyst for the selective hydroformylation of 1-olefins to produce aldehydes at low pressures and mild temperatures. The selectivity for n-aldehydes increases in the presence of excess PPh₃ and at low CO partial pressures.^[1] The first step in the hydroformylation process is the dissociative substitution of an alkene for a PPh₃. The migratory insertion of this 18-electron complex can result in either a primary or secondary rhodium alkyl. This step sets the regiochemistry of the product, however it is rapidly reversible. The 16-electron alkyl complex undergoes migratory insertion of a CO to form the coordinately unsaturated acyl. This species once again gives an 18-electron acyl complex.^[6] The last step involves β-H elimination via hydrogenolysis which results in the cleavage of the aldehyde product and regeneration of the rhodium catalyst.

References

^ ^a ^b J. F. Hartwig; Organotransition metal chemistry - from bonding to catalysis. University Science Books. 2009. 753, 757-578. ISBN 978-1-891-38953-5.
^ Ahmad, N.; Levison, J. J.; Robinson, S. D.; Uttley, M. F. (1990). "Hydrido Phosphine Complexes of Rhodium(I)". Inorganic Syntheses. Vol. 28. pp. 81–83. doi:10.1002/9780470132593.ch19. ISBN 9780470132593.
^ I. S. Babra, L. S. Morley, S. C. Nyburg, A. W. Parkins "The crystal and molecular structure of a new polymorph of a carbonlyhydridotris(triphenylphosphine)rhodium(I) having a Rh-H stretching absorption at 2013 cm⁻¹" Journal of Crystallographic and Spectroscopic Research 23. 1993. 999. doi:10.1007/BF01185550.
^ S. J. la Placa, J. A. Ibers "Crystal and Molecular Structure of Tristriphenylphosphine Rhodium Carbonyl Hydride" Acta Crystallogr. 1965, p. 511. doi:10.1107/S0365110X65001093
^ D. Evans, J. A. Osborn, G. Wilkinson "Hydroformylation of Alkenes by Use of Rhodium Complex Catalysts" J. Chem. Soc. 1968, pp. 3133-3142. doi:10.1039/J19680003133
^ R. V. Kastrup, J. S. Merola, A. A. Oswald; P-31 NMR Studies of Equilibria and Ligand Exchange in Triphenylphosphine Rhodium Complex and Related Chelated Bisphosphine Rhodium Complex Hydroformylation Catalyst Systems. J. Am. Chem. Soc. 1982.44-16. doi:10.1021/ba-1982-0196.ch003.