Reaction of Nitrogen Chelates with the [Rh2]4+ Core: Bis-Chelate Products and Demonstration of Reversible, Chelate-Based Reduction Processes
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- 作者：Charles A. Crawford ; John H. Matonic ; John C. Huffman ; Kirsten Folting ; Kim R. Dunbar ; and George Christou
- 刊名：Inorganic Chemistry
- 出版年：1997
- 出版时间：May 21, 1997
- 年：1997
- 卷：36
- 期：11
- 页码：2361 - 2371
- 全文大小：285K
- 年卷期：v.36,no.11(May 21, 1997)
- ISSN：1520-510X
文摘
The preparations and properties are described of a series of[Rh2]4+ complexes possessing carboxylatesand N-basedchelates as ligands. Treatment ofRh2(O2CR)4(MeOH)2(R = Me (1), Et (2), Ph (3) orCF3 (4)) with 2 equiv of2,2'-bipyridine (bpy) in refluxing MeCN leads to the[Rh2(O2CR)2(bpy)2]2+cation (in complexes 5-9).Reactionof 1 with 1,10-phenanthroline (phen),4,4'-dimethyl-2,2'-bipyridine (Me2bpy),4,4'-diphenyl-2,2'-bipyridine (Ph2bpy), and 4,7-diphenyl-1,10-phenanthroline(Ph2phen) leads to the analogous cations of complexes10-13.Complex 6a,[Rh2(OAc)2(bpy)2(MeCN)2](PF6)2·2MeCN,crystallizes in monoclinic space groupP21/a with thefollowing cell parameters at -172 
C: a =14.433(2) Å, b = 12.810(1) Å, c =22.78(3) Å, 
= 104.42(3), Z= 4, and V = 3971.2 Å3. Complex9,[Rh2(O2CCF3)4(bpy)2]·Me2CO,crystallizes in triclinic space group P
with the following cell parameters at 20 C: a =14.260(4) Å, b = 15.375(4) Å, c =9.709(2) Å, 
= 105.98(2), = 97.49(2), 
= 70.32(2), Z = 2,and V = 1925.2 Å3. Both 6aand 9 contain a singly-bonded[Rh2]4+ unitwith two cis bridging RCO2- groupsand two syn-bpy chelate groups in a near-eclipsedconformation about theRh-Rh vector. Reaction of[Rh2(tpy)2(MeCN)4](BF4)4(15) (tpy = 2,2':6',2''-terpyridine) withNBun4(O2CPh)gives[Rh2(O2CPh)(tpy)2(MeCN)2](BF4)3·MeCN(16). Complex 16 crystallizes in triclinicspace group P withthe following cell parameters at -168 C: a =11.684(4) Å, b = 20.373(8) Å, c =10.451(3) Å, = 93.47(2), = 110.53(1), = 100.03(2), Z =2, and V = 2274.1 Å3. The cation of16 consists of a [Rh2]4+ unitwith abridging PhCO2- group and two chelating tpygroups. The solution 1H NMR properties of complexes6-13 and16 show the complexes to retain their solid-state structureson dissolution. The electrochemical properties of6-13 and 16 were investigated bycyclic voltammetry (CV) and differential pulse voltammetry (DPV) inMeCN.The bis(bpy) and -(phen) complexes6-8, 10, and 11 show areversible, one-electron reduction in the range-0.83 to -0.91 V vs ferrocene and an additional,irreversible reduction and an irreversible oxidation; thePh2bpy(12) and Ph2phen (13) complexesshow a two-electron reversible reduction at -0.61 to -0.76 and areversibleone-electron oxidation at 0.68-0.89 V. Consideration of thepotentials as a function of carboxylate and chelateidentity leads to the conclusion that the reductions are ligand(chelate)-based. This is supported by an extendedHückel calculation on the model compound[Rh2(O2CH)2(bpy)2(HCN)2]2+,which shows the LUMO to be a bpy-based orbital comprising in-phase, 
overlap of two bpy 
* orbitals,one on each of the syn-bpy groups. Incontrast, complex 16 shows no reversible reductionprocesses. Complex 6b,[Rh2(OAc)2(bpy)2(MeCN)2](BF4)2,in MeCN may be reduced with sodium acenaphthylenide in THF to give deepblue[Rh2(OAc)2(bpy)2(MeCN)2](BF4) (14) in high yield. The cation of14 may also be generated by controlled potentialelectrolysis of 6a inMeCN at -0.99 V and by heating of a solution of 6a or6b in alcohol.
C: a =14.433(2) Å, b = 12.810(1) Å, c =22.78(3) Å, = 104.42(3), Z= 4, and V = 3971.2 Å3. Complex9,[Rh2(O2CCF3)4(bpy)2]·Me2CO,crystallizes in triclinic space group Pwith the following cell parameters at 20 C: a =14.260(4) Å, b = 15.375(4) Å, c =9.709(2) Å, = 105.98(2), = 97.49(2), = 70.32(2), Z = 2,and V = 1925.2 Å3. Both 6aand 9 contain a singly-bonded[Rh2]4+ unitwith two cis bridging RCO2- groupsand two syn-bpy chelate groups in a near-eclipsedconformation about theRh-Rh vector. Reaction of[Rh2(tpy)2(MeCN)4](BF4)4(15) (tpy = 2,2':6',2''-terpyridine) withNBun4(O2CPh)gives[Rh2(O2CPh)(tpy)2(MeCN)2](BF4)3·MeCN(16). Complex 16 crystallizes in triclinicspace group P withthe following cell parameters at -168 C: a =11.684(4) Å, b = 20.373(8) Å, c =10.451(3) Å, = 93.47(2), = 110.53(1), = 100.03(2), Z =2, and V = 2274.1 Å3. The cation of16 consists of a [Rh2]4+ unitwith abridging PhCO2- group and two chelating tpygroups. The solution 1H NMR properties of complexes6-13 and16 show the complexes to retain their solid-state structureson dissolution. The electrochemical properties of6-13 and 16 were investigated bycyclic voltammetry (CV) and differential pulse voltammetry (DPV) inMeCN.The bis(bpy) and -(phen) complexes6-8, 10, and 11 show areversible, one-electron reduction in the range-0.83 to -0.91 V vs ferrocene and an additional,irreversible reduction and an irreversible oxidation; thePh2bpy(12) and Ph2phen (13) complexesshow a two-electron reversible reduction at -0.61 to -0.76 and areversibleone-electron oxidation at 0.68-0.89 V. Consideration of thepotentials as a function of carboxylate and chelateidentity leads to the conclusion that the reductions are ligand(chelate)-based. This is supported by an extendedHückel calculation on the model compound[Rh2(O2CH)2(bpy)2(HCN)2]2+,which shows the LUMO to be a bpy-based orbital comprising in-phase, overlap of two bpy * orbitals,one on each of the syn-bpy groups. Incontrast, complex 16 shows no reversible reductionprocesses. Complex 6b,[Rh2(OAc)2(bpy)2(MeCN)2](BF4)2,in MeCN may be reduced with sodium acenaphthylenide in THF to give deepblue[Rh2(OAc)2(bpy)2(MeCN)2](BF4) (14) in high yield. The cation of14 may also be generated by controlled potentialelectrolysis of 6a inMeCN at -0.99 V and by heating of a solution of 6a or6b in alcohol.