Lindner Ronald, Wagner Christoph, Steinborn Dirk
Institut für Chemie-Anorganische Chemie, Martin-Luther-Universität, Kurt-Mothes-Strasse 2, D-06120 Halle, Germany.
J Am Chem Soc. 2009 Jul 1;131(25):8861-74. doi: 10.1021/ja901264t.
Reactions of the platinum(IV) complexes PtMe(3)(OCMe(2))(3) (1(BF(4))), [(PtMe(3)I)(4)] (2), and [PtMe(3)I(py)(2)] (3) with the N,N-heterocyclic carbene 1,3-dimethylimidazol-2-ylidene (N,N-hc, 4) resulted in a rapid reductive elimination of ethane, yielding platinum(II) complexes PtMe(N,N-hc)(3) (7), trans-[PtMeI(N,N-hc)(2)] (8), and cis-PtMe(py)(N,N-hc)(2) (10), respectively. Subsequent substitution of the iodo ligand in 8 by pyridine resulted in the formation of trans-PtMe(py)(N,N-hc)(2) (9(CF(3)COO)). 9 and 10 are stereoisomers. In contrast to this, the analogous reaction of PtMe(3)(OCMe(2))(3) (1(BF(4))) with the N,O-heterocyclic carbene 3-methyloxazol-2-ylidene (N,O-hc, 5) was found to yield the tris(carbene)trimethylplatinum(IV) compound PtMe(3)(N,O-hc)(3) (12(BF(4))), which is thermally stable up to 218 degrees C in the solid state. Furthermore, reactions of [{PtMe(3)(acac)}(2)] (15) with the N,X-heterocyclic carbenes (X = N, O, S; N,S-hc = 3-methylthiazol-2-ylidene, 6) resulted in the formation of monocarbenetrimethylplatinum(IV) complexes [PtMe(3)(acac)(N,X-hc)] (X = N, 16; X = O, 17; X = S, 18), which were found to be stable against reductive C-C elimination at ambient temperature. Reactions of 16 and 17 with 2,2'-bipyridine (bpy) in the presence of stoichiometric amounts of H(BF(4)) yielded cationic monocarbeneplatinum(IV) complexes, which were isolated as tetrafluoroborate salts PtMe(3)(bpy)(N,X-hc) (X = N, 19(BF(4)); X = O, 20(BF(4))). The compounds have been fully characterized analytically and NMR spectroscopically, and for the bis(carbene)platinum(II) compound 9(CF(3)COO) as well as the monocarbeneplatinum(IV) compounds 16 and 20(BF(4)) by single-crystal X-ray diffraction analyses. DFT calculations of mono-, bis-, and tris(carbene)trimethylplatinum(IV) complexes and their propensity to reductive eliminate ethane were performed. In accordance with the experimental findings, a much higher stability of the tris(N,O-hc)- compared with the tris(N,N-hc)trimethylplatinum(IV) complexes against reductive ethane elimination was found, which could be ascribed mainly to a higher steric demand of the N,N-hc ligand.
铂（IV）配合物PtMe(3)(OCMe(2))(3)（1(BF(4))）、[(PtMe(3)I)(4)]（2）和[PtMe(3)I(py)(2)]（3）与N，N - 杂环卡宾1,3 - 二甲基咪唑 - 2 - 亚基（N，N - hc，4）反应，迅速发生乙烷的还原消除反应，分别生成铂（II）配合物[PtMe(N，N - hc)(3)]⁺（7）、反式 - [PtMeI(N，N - hc)(2)]（8）和顺式 - [PtMe(py)(N，N - hc)(2)]⁺（10）。随后，8中的碘配体被吡啶取代，生成反式 - PtMe(py)(N，N - hc)(2)（9(CF(3)COO)）。9和10是立体异构体。与此相反，发现PtMe(3)(OCMe(2))(3)（1(BF(4))）与N，O - 杂环卡宾3 - 甲基恶唑 - 2 - 亚基（N，O - hc，5）的类似反应生成三（卡宾）三甲基铂（IV）化合物PtMe(3)(N，O - hc)(3)（12(BF(4))），该化合物在固态下热稳定性高达218℃。此外，[{PtMe(3)(acac)}(2)]（15）与N，X - 杂环卡宾（X = N，O，S；N，S - hc = 3 - 甲基噻唑 - 2 - 亚基，6）反应生成单卡宾三甲基铂（IV）配合物[PtMe(3)(acac)(N，X - hc)]（X = N，16；X = O, 17；X = S，18），发现它们在室温下对C - C还原消除稳定。16和17与2,2'-联吡啶（bpy）在化学计量的H(BF(4))存在下反应，生成阳离子单卡宾铂（IV）配合物，以四氟硼酸盐PtMe(3)(bpy)(N，X - hc)（X = N，19(BF(4))；X = O，20(BF(4))）形式分离得到。这些化合物已通过元素分析和核磁共振光谱进行了全面表征，对于双（卡宾）铂（II）化合物9(CF(3)COO)以及单卡宾铂（IV）化合物16和20(BF(4))还通过单晶X射线衍射分析进行了表征。对单、双和三（卡宾）三甲基铂（IV）配合物及其还原消除乙烷的倾向进行了密度泛函理论计算。与实验结果一致，发现三（N，O - hc） - 三甲基铂（IV）配合物相对于三（N，N - hc） - 三甲基铂（IV）配合物对乙烷还原消除具有更高的稳定性，这主要归因于N，N - hc配体更高的空间需求。
