Synthetic Endeavors toward Titanium Based Frustrated Lewis Pairs with Controlled Electronic and Steric Properties

A new family of cationic
Ti complexes 4′ with
a pendant phosphine of general formula [CpCpPTiOAr]­[BPh4] (Cp = η5-C5H5; CpP = η5-C5H4(CMe2)­PR2) has been prepared in four steps from 6,6-dimethylfulvene.
These complexes were designed to behave as Ti based frustrated Lewis
pairs (FLPs). The key synthetic step is a reduction–oxidation
sequence from [CpCpPTiClOAr] complexes 3 using lithium phosphide salts as
the reductants and ferricinium tetraphenylborate as the oxidant. Four
complexes have been structurally characterized by X-ray diffraction
and show elongated Ti–P bonds, above 2.60 Å. One complex
(4b′: OAr = 2,6-Me2C6H3; PR2 = PCy2) reacted with benzaldehyde
to form a typical FLP activation product. Complex 4b′
also reacted with 2 equiv of trans-chalcone to form
a 10-membered Ti phosphonium macrocycle (6b′)
by extrusion of 6,6-dimethylfulvene.

一种新型的阳离子Ti复合物4'系列，其侧链磷原子具有通式[CpCpPTiOAr][BPh4]（Cp = η5-C5H5；CpP = η5-C5H4(CMe2)PR2），已通过四步反应从6,6-二甲基富勒烯合成。这些复合物被设计为基于Ti的受阻路易斯对（FLPs）。关键的合成步骤是通过使用磷化锂盐作为还原剂和铁氰酸四苯硼酯作为氧化剂，从[CpCpPTiClOAr]复合物3中进行还原-氧化序列。四个复合物通过X射线衍射进行了结构表征，显示出大于2.60 Å的延长Ti-P键。其中一种复合物（4b'：OAr = 2,6-二甲基苯；PR2 = PCy2）与苯甲醛反应，生成了典型的FLP激活产物。复合物4b'还与2当量的反式查耳酮反应，通过6,6-二甲基富勒烯的挤出，形成了一个10元Ti磷阳离子大环（6b'）。