Organorhodium chemistry

Organorhodium chemistry is the chemistry of organometallic compounds containing a carbon to rhodium chemical bond, and the study of rhodium and rhodium compounds as catalysts in organic reactions.^[1]

Organometallic rhodium compounds share many characteristics with those of cobalt (see organocobalt compounds) in the same group 9. Rhodium can exist in oxidation states +IV to -III but +I and +III are the most common. Rhodium(I) compounds (d⁸ configuration) can occur with square planar geometries and with trigonal bipyramidal geometries. Important homoleptic rhodium compounds are tetrarhodium dodecacarbonyl Rh₄(CO)₁₀ and hexadecacarbonylhexarhodium Rh₆(CO)₁₆. The hexarhodium compound is less preferred due to poor solubility. Both are important catalysts in hydroformylation of alkenes often accompanied by a phosphine ligand:

$\mathrm{RHC=CH_2\ %2B\ CO\ %2B\ H_2\ \xrightarrow {Rh_4(CO)_{10} / PPh_3}\ \ RCH_2CH_2CHO}$

Nitrobenzene reduction is another reaction catalysed by this compound type:

$\mathrm{PhNO_2\ %2B\ C_6H_6\ %2B\ 3\ CO\ \xrightarrow {Rh_6(CO)_{16}}\ \ PhNHCOPh\ %2B\ 2\ CO_2}$

Cyclooctadiene rhodium chloride dimer [RhCl(COD)]₂ is investigated for its use in C-H bond activation. Sandwich compounds of rhodium, such as rhodocene, and half-sandwich compounds like [(η⁵-Cp)Rh(CO)₂] are well known.

Other relevant organorhodium compounds used as catalysts
Name	Molecular formula	CAS
(Acetylacetonato)dicarbonylrhodium(I)	Rh(CO)₂(C₅H₇O₂)	14874-82-9
Bicyclo[2.2.1]hepta-2,5-diene-rhodium(I) chloride dimer	C₁₄H₁₆Cl₂Rh₂	12257-42-0
Chloro(1,5-cyclooctadiene)rhodium(I) dimer	C₁₆H₂₄Cl₂Rh₂	12092-47-6
(Acetylacetonato)(norbornadiene)rhodium(I)	C₁₂H₁₅O₂2Rh	32354-50-0
Chloro(1,5-hexadiene)rhodium(I),dimer	C₁₂H₂₄Rh₂Cl₂	32965-49-4
Acetylacetonatobis(ethylene)rhodium(I)	C₉H₁₅O₂Rh	12082-47-2
[1,4-Bis(diphenylphosphino)butane](1,5-cyclooctadiene)rhodium(I) tetrafluoroborate	C₃₆H₄₀BF₄P₂Rh	79255-71-3

Cyclometallation

Cyclometalated rhodium compounds constitute an important class of organometallic chemistry. Although such compounds are well documented in the literature rhodium(III) cyclometalates with azo function are spare. A typical example of this category viz. novel hexacoordinated orthometalated rhodium(III) thiolato complex trans-[Rh(C^∧N^∧S)Cl(PPh₃)₂] was synthesized from benzyl 2-(phenylazo)phenyl thioether and RhCl₃·3H₂O in the presence of excess PPh₃ via in situ C(sp²)−H and C(sp³)−S bond scissions. This is the first example for a coordination compound of (phenylazo)thiolate ligand. The mechanism of formation of orthometalated azobenzene derivative was described to proceed via initial coordination of azo-nitrogen followed by electrophilic substitution at the pendant phenyl ring. PPh₃ plays a crucial role in the C(sp³)−S cleavage process. Reductive cleavage by single electron transfer (SET) mechanism is likely to be operative for the C−S bond cleavage. Unlike analogous (phenylazo)phenolato compound the orthometalated thiolato complex exhibits a fully reversible oxidative wave at 0.82 V vs Ag/AgCl and this response is supposed to be primarily centered on the thiolato sulfur atom.^[2]

CH				He
CLi	CBe	CB	CC	CN	CO	CF	Ne
CNa	CMg	CAl	CSi	CP	CS	CCl	CAr
CK	CCa	CSc	CTi	CV	CCr	CMn	CFe	CCo	CNi	CCu	CZn	CGa	CGe	CAs	CSe	CBr	CKr
CRb	CSr	CY	CZr	CNb	CMo	CTc	CRu	CRh	CPd	CAg	CCd	CIn	CSn	CSb	CTe	CI	CXe
CCs	CBa		CHf	CTa	CW	CRe	COs	CIr	CPt	CAu	CHg	CTl	CPb	CBi	CPo	CAt	Rn
Fr	Ra	Rf	Db	Sg	Bh	Hs	Mt	Ds	Rg	Cn	Uut	Uuq	Uup	Uuh	Uus	Uuo
	↓
	CLa	CCe	CPr	CNd	CPm	CSm	CEu	CGd	CTb	CDy	CHo	CEr	CTm	CYb	CLu
	Ac	Th	Pa	CU	Np	Pu	Am	Cm	Bk	Cf	Es	Fm	Md	No	Lr

**Chemical bonds to carbon**
Core organic chemistry	Many uses in chemistry
Academic research, but no widespread use	Bond unknown / not assessed

References

^ Synthesis of Organometallic Compounds: A Practical Guide Sanshiro Komiya Ed. S. Komiya, M. Hurano 1997
^ K. Pramanik, U. Das, B. Adhikari, D. Chopra, H. Stoeckli-Evans (2008). "RhCl₃-Assisted C-H and C-S Bond Scissions: Isomeric Self-Association of Organorhodium(III) Thiolato Complex. Synthesis, Structure, and Electrochemistry". Inorg. Chem. 47 (2): 429–438. doi:10.1021/ic7016006. PMID 18161963.

CH																	He
CLi	CBe											CB	CC	CN	CO	CF	Ne
CNa	CMg											CAl	CSi	CP	CS	CCl	CAr
CK	CCa	CSc	CTi	CV	CCr	CMn	CFe	CCo	CNi	CCu	CZn	CGa	CGe	CAs	CSe	CBr	CKr
CRb	CSr	CY	CZr	CNb	CMo	CTc	CRu	CRh	CPd	CAg	CCd	CIn	CSn	CSb	CTe	CI	CXe
CCs	CBa		CHf	CTa	CW	CRe	COs	CIr	CPt	CAu	CHg	CTl	CPb	CBi	CPo	CAt	Rn
Fr	Ra		Rf	Db	Sg	Bh	Hs	Mt	Ds	Rg	Cn	Uut	Uuq	Uup	Uuh	Uus	Uuo
		↓
		CLa	CCe	CPr	CNd	CPm	CSm	CEu	CGd	CTb	CDy	CHo	CEr	CTm	CYb	CLu
		Ac	Th	Pa	CU	Np	Pu	Am	Cm	Bk	Cf	Es	Fm	Md	No	Lr

CH																	He
CLi	CBe											CB	CC	CN	CO	CF	Ne
CNa	CMg											CAl	CSi	CP	CS	CCl	CAr
CK	CCa	CSc	CTi	CV	CCr	CMn	CFe	CCo	CNi	CCu	CZn	CGa	CGe	CAs	CSe	CBr	CKr
CRb	CSr	CY	CZr	CNb	CMo	CTc	CRu	CRh	CPd	CAg	CCd	CIn	CSn	CSb	CTe	CI	CXe
CCs	CBa		CHf	CTa	CW	CRe	COs	CIr	CPt	CAu	CHg	CTl	CPb	CBi	CPo	CAt	Rn
Fr	Ra		Rf	Db	Sg	Bh	Hs	Mt	Ds	Rg	Cn	Uut	Uuq	Uup	Uuh	Uus	Uuo
		↓
		CLa	CCe	CPr	CNd	CPm	CSm	CEu	CGd	CTb	CDy	CHo	CEr	CTm	CYb	CLu
		Ac	Th	Pa	CU	Np	Pu	Am	Cm	Bk	Cf	Es	Fm	Md	No	Lr

Organorhodium chemistry

Cyclometallation

See also

References

CH																	He
CLi	CBe											CB	CC	CN	CO	CF	Ne
CNa	CMg											CAl	CSi	CP	CS	CCl	CAr
CK	CCa	CSc	CTi	CV	CCr	CMn	CFe	CCo	CNi	CCu	CZn	CGa	CGe	CAs	CSe	CBr	CKr
CRb	CSr	CY	CZr	CNb	CMo	CTc	CRu	CRh	CPd	CAg	CCd	CIn	CSn	CSb	CTe	CI	CXe
CCs	CBa		CHf	CTa	CW	CRe	COs	CIr	CPt	CAu	CHg	CTl	CPb	CBi	CPo	CAt	Rn
Fr	Ra		Rf	Db	Sg	Bh	Hs	Mt	Ds	Rg	Cn	Uut	Uuq	Uup	Uuh	Uus	Uuo
		↓
		CLa	CCe	CPr	CNd	CPm	CSm	CEu	CGd	CTb	CDy	CHo	CEr	CTm	CYb	CLu
		Ac	Th	Pa	CU	Np	Pu	Am	Cm	Bk	Cf	Es	Fm	Md	No	Lr