Rhodium(III) Peroxo Complexes Containing Carbene and Phosphine Ligands

The Rh(I) carbene precursors [RhCl(COE)(NHC)]2, where the N-heterocyclic carbene is 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) or 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes),
were used to synthesize the RhCl(NHC)(P-N) complexes 4 (NHC = IPr) and 5 (NHC = IMes), where
P-N is P,N-chelated o-(diphenylphosphino)-N,N-dimethylaniline, and the corresponding cis-RhCl(NHC)(PPh3)2 complexes 6 and 7. The synthesis of 4 surprisingly requires the reaction to be carried out under
a hydrogen atmosphere and occurs via the intermediate dihydride RhCl(H)2(IPr)(P-N) (3). Complexes
4−7 in benzene readily undergo irreversible oxidative addition of O2 to form the corresponding Rh(III)
peroxide complexes 9−12. For comparative purposes, RhCl(PPh3)(P-N) (8) was synthesized from RhCl(PPh3)3, and this also added O2 to form a peroxo complex (13). All of the complexes were generally
characterized by elemental analysis and 1H, 31P{1H}, and 13C{1H} NMR and IR spectroscopies and, in
the cases of 9, 10, and 13, by X-ray crystallography.

以铑(I)卡宾前体[RhCl(COE)(NHC)]₂为起始原料，其中N-杂环卡宾（N-heterocyclic carbene, NHC）为1,3-双(2,6-二异丙基苯基)咪唑-2-亚基（IPr）或1,3-双(2,4,6-三甲基苯基)咪唑-2-亚基（IMes），成功合成了RhCl(NHC)(P-N)型配合物4（NHC=IPr）与5（NHC=IMes），以及对应的顺式-RhCl(NHC)(PPh₃)₂型配合物6和7；此处P-N指代P,N-螯合邻-(二苯基膦基)-N,N-二甲基苯胺。
配合物4的合成出乎意料地需要在氢气氛围中进行，反应经由中间体二氢化物RhCl(H)₂(IPr)(P-N)（3）完成。
苯溶剂中的配合物4至7可快速发生不可逆的O₂氧化加成反应，生成对应的铑(III)过氧化物配合物9至12。
为开展对比研究，以RhCl(PPh₃)₃为原料合成了RhCl(PPh₃)(P-N)（8），该配合物同样可与O₂反应生成过氧配合物13。
所有配合物均通过元素分析、¹H、³¹P{¹H}及¹³C{¹H}核磁共振波谱与红外光谱完成表征，其中配合物9、10与13还通过X射线晶体学进行了结构确证。