Technische Universität München, Department Chemie, Lichtenbergstr. 4, 85747 Garching b, München, Germany.
Inorg Chem. 2010 Jun 21;49(12):5482-94. doi: 10.1021/ic100358m.
The quantitative formation of enamido complex [Ru(H)PMe(3)(PNP')] (3; PNP' = N(CHCHP(i)Pr(2))(CH(2)CH(2)P(i)Pr(2))) from the reaction of [RuCl(2)PMe(3)(HPNP)] (5; HPNP = HN(CH(2)CH(2)P(i)Pr(2))(2)) with an excess of base (KOtBu) can be explained by beta-hydride migration from an intermediate amido complex [RuClPMe(3)(PNP)] (6; PNP = N(CH(2)CH(2)P(i)Pr(2))(2)). Resulting imine complex [RuCl(H)PMe(3)(PNP*)] (7; PNP* = N(CHCH(2)P(i)Pr(2))(CH(2)CH(2)P(i)Pr(2))) could be independently synthesized and gives 3 with KOtBu. A computational examination of the reversible double H(2) addition and elimination equilibria of enamide 3, amido complex [Ru(H)PMe(3)(PNP)] (1), and amine complex [Ru(H)(2)PMe(3)(HPNP)] (2) explains why [Ru(H)(2)PMe(3)(PNP*)] (8) is not observed experimentally. The distinctly different molecular and electronic structures of related complexes 1 and 3, which feature a Y-shaped distorted trigonal-bipyramid (Y-TBP) for amide 1 but T-shaped TBP for enamide 3, respectively, can be attributed to considerably reduced N-->M pi-donation for the PNP' ligand due to delocalization of the N-lone pair into the unsaturated pincer backbone. The resulting low-lying LUMO of 3 explains its Lewis-acidic behavior, as documented by the formation of octahedral complex [RuH(PMe(3))(2)(PNP')] (14) upon the addition of PMe(3). In comparison, the reaction of 1 with PMe(3) gives a mixture of 2 and 14 via a base-assisted hydrogen elimination pathway. On the other hand, with electrophiles, such as MeOTf, predominant N-methylation is observed for both 1 and 3, producing [RuH(OTf)PMe(3)(MePNP)] (11) and [RuH(OTf)PMe(3)(MePNP')] (12), respectively. This reactivity of 3 contrasts with pyridine-based cooperative pincer analogues and can be attributed to the high flexibility of the aliphatic PNP' pincer ligand. The structural and reactivity patterns place this novel ligand between the parent PNP and aromatic pincer ligands.
从 [RuCl2PMe3(HPNP)]（5；HPNP = HN(CH2CH2P(i)Pr2)(2)）与过量碱（KOtBu）反应定量生成 enamido 配合物[Ru(H)PMe3(PNP')]（3；PNP' = N(CHCHP(i)Pr(2))(CH(2)CH(2)P(i)Pr(2)))）可以解释为β-氢化物从中间酰胺配合物[RuClPMe3(PNP)]（6；PNP = N(CH2CH2P(i)Pr2)(2)）迁移。得到的亚胺配合物[RuCl(H)PMe3(PNP*)]（7；PNP* = N(CHCH2P(i)Pr2)(CH2CH2P(i)Pr2)）可以独立合成，并与 KOtBu 反应生成 3。对烯酰胺 3、酰胺配合物[Ru(H)PMe3(PNP)]（1）和胺配合物[Ru(H)2PMe3(HPNP)]（2）的可逆双 H2 加成和消除平衡的计算研究解释了为什么实验中未观察到[Ru(H)2PMe3(PNP*)]（8）。相关配合物 1 和 3 的分子和电子结构明显不同，酰胺 1 具有 Y 形扭曲三角双锥（Y-TBP），而烯酰胺 3 具有 T 形 TBP，分别归因于 PNP'配体的 N->M π 供体显著减少，因为 N-孤对电子离域到不饱和钳形骨架中。3 的低占据 LUMO 解释了其路易斯酸性行为，这一点通过添加 PMe3 形成八面体配合物[RuH(PMe3)2(PNP')]（14）得到证实。相比之下，1 与 PMe3 的反应通过碱辅助的氢消除途径得到 2 和 14 的混合物。另一方面，对于亲电试剂，如 MeOTf，1 和 3 都观察到主要的 N-甲基化，生成[RuH(OTf)PMe3(MePNP)]（11）和[RuH(OTf)PMe3(MePNP')]（12）。3 的这种反应性与基于吡啶的协同钳形类似物形成对比，这归因于脂肪族 PNP'钳形配体的高灵活性。结构和反应性模式将这种新型配体置于母体 PNP 和芳香族钳形配体之间。
