Hexadecacarbonylhexarhodium

Hexadecacarbonylhexarhodium is a metal carbonyl cluster with the formula Rh₆(CO)₁₆. It exists as purple-brown crystals that are slightly soluble in dichloromethane and chloroform.^[1] It is the principal binary carbonyl of rhodium.

Hexadecacarbonylhexarhodium

Names
IUPAC name Hexadecacarbonylhexarhodium
Other names Hexarhodium hexadecacarbonyl
Identifiers
CAS Number	28407-51-4 Y[ECHA]
3D model (JSmol)	Interactive image
ChemSpider	9041327
ECHA InfoCard	100.044.539
EC Number	249-009-3
PubChem CID	10866043
CompTox Dashboard (EPA)	DTXSID10951074
InChI InChI=1S/16CO.6Rh/c16*1-2;;;;;; Key: SZQABOJVTZVBHE-UHFFFAOYSA-N
SMILES [C-]#[O+].[C-]#[O+].[C-]#[O+].[C-]#[O+].[C-]#[O+].[C-]#[O+].[C-]#[O+].[C-]#[O+].[C-]#[O+].[C-]#[O+].[C-]#[O+].[C-]#[O+].[C-]#[O+].[C-]#[O+].[C-]#[O+].[C-]#[O+].[Rh].[Rh].[Rh].[Rh].[Rh].[Rh]
Properties
Chemical formula	C16O16Rh6
Molar mass	1065.62 g/mol
Appearance	purple-brown solid
Melting point	235 °C (455 °F; 508 K)
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H302, H312, H332
Precautionary statements	P261, P264, P270, P271, P280, P301+P312, P302+P352, P304+P312, P304+P340, P312, P322, P330, P363, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Discovery and synthesis

Rh₆(CO)₁₆ was first prepared by Walter Hieber in 1943 by carbonylation of RhCl₃·3H₂O at 80–230 °C and 200 atm carbon monoxide with silver or copper as a halide acceptor. Hieber correctly formulated the compound as a binary carbonyl, but suggested the formula Rh₄(CO)₁₁, i.e., CO/Rh ratio of 2.75.^[2] The correct formula and structure was subsequently established by Dahl et al. using X-ray crystallography. The correct CO/Rh ratio is 2.66.^[3]

Relative to the original preparation, the carbonylation of a mixture of anhydrous rhodium trichloride and iron pentacarbonyl was shown to give good yields of Rh₆(CO)₁₆.^[4] Other compounds of rhodium are also effective precursors such as [(CO)₂Rh(μ-Cl)]₂ and rhodium(II) acetate:^[1]

3 Rh₂(O₂CCH₃)₄ + 22 CO + 6 H₂O → Rh₆(CO)₁₆ +  6 CO₂ + 12 CH₃COOH

3 [(CO)₂RhCl]₂ + 4 CO + 6 Cu → Rh₆(CO)₁₆ + 6 CuCl

It also arises quantitatively by thermal decomposition of tetrarhodium dodecacarbonyl in boiling hexane:^[5]

3 Rh₄(CO)₁₂ → 2 Rh₆(CO)₁₆ + 4 CO

Reactions

At least some of the CO ligands can be displaced by donor ligands.^[5]

Rh₆(CO)₁₆ catalyzes a number of organic reactions including hydrogenation and hydroformylation.^[4]