Controlled Synthesis of a Structurally Characterized Family of Sterically Constrained Heterocyclic Alkoxy-Modified Titanium Alkoxides

The reaction of [Ti(μ-ONep)(ONep)3]2 (ONep = OCH2C(CH3)3) with a series of heterocyclic methanol derivatives
[tetrahydrofurfuryl alcohol (H−OTHF), thiophene methanol (H−OTPM), or 2-pyridylcarbinol (H−OPy)collectively
termed H−OR*], led to the isolation of a novel family of OR*-substituted titanium alkoxide precursors. Independent
of the initial stoichiometry for the H−OTHF reaction, a monosubstituted, dinuclear species was isolated as [(ONep)3Ti(μc-OTHF)]2 (1). For 1, each Ti was octahedrally (Oh) bound by three terminal ONep ligands, one bidentate bridging
OTHF ligand (μc-OTHF), and an oxygen from the other μc-OTHF ligand. For the OTPM derivatives, the product
was identified as [(ONep)3Ti(μ-OTPM)]2 (2). For this ligand, the soft S atom does not bind to the Ti but the O atom
does act as a bridge between the two trigonal bipyramidal bound Ti metal centers. The OPy system yielded
(OPy)2Ti(OR)2 independent of the OR and the stoichiometry used [OR = ONep (3), OCHMe2 (4), OCMe3 (5)]. For
3−5, the two OPy ligands chelate to the Oh-bound Ti metal center with two terminal OR ligands. Compounds 1−5
were fully characterized using a variety of analytical techniques. An initial investigation of the proposed chemical
stability of the ‘(OPy)2Ti' moiety of 3−5 to alcoholysis exchange pathways involving (i) alkyl alcohols, (ii) aryl alcohols,
(iii) substituted phenols, (iv) H−OR* derivatives, and (v) silanols proved successful through the isolation of a novel
family of structurally characterized (OPy)2Ti(OR‘)2 (7−24) compounds.

二(μ-新戊氧基)三(新戊氧基)钛二聚体[Ti(μ-ONep)(ONep)₃]₂（其中ONep = OCH₂C(CH₃)₃）与一系列杂环甲醇衍生物[四氢糠醇（tetrahydrofurfuryl alcohol, H−OTHF）、噻吩甲醇（thiophene methanol, H−OTPM）或2-吡啶甲醇（2-pyridylcarbinol, H−OPy），统称为H−OR*]发生反应，成功分离得到一类新型的OR*取代钛醇盐前驱体。无论四氢糠醇（H−OTHF）参与反应的初始化学计量比如何，均能分离得到单取代双核物种[(ONep)₃Ti(μc-OTHF)]₂（1）。对于化合物1，每个钛原子均以八面体（Oh）配位模式结合3个端基ONep配体、1个双齿桥联OTHF配体（μc-OTHF），以及另一个μc-OTHF配体中的氧原子。对于噻吩甲醇（OTPM）衍生物，产物鉴定为[(ONep)₃Ti(μ-OTPM)]₂（2）。该配体中软碱性的硫原子并未与钛结合，仅氧原子作为桥联基团连接两个以三角双锥配位模式结合的钛金属中心。而2-吡啶甲醇（OPy）体系的产物为(OPy)₂Ti(OR)₂，与所用的OR基团及反应化学计量比无关[其中OR = ONep（3）、OCHMe₂（4）、OCMe₃（5）]。对于化合物3~5，两个OPy配体与八面体配位的钛金属中心发生螯合，同时结合2个端基OR配体。采用多种分析技术对化合物1~5进行了全面表征。针对化合物3~5中“(OPy)₂Ti”结构单元在涉及(i)烷基醇、(ii)芳基醇、(iii)取代酚、(iv)H−OR*衍生物以及(v)硅醇的醇解交换反应路径中的预期化学稳定性开展初步探究，最终通过分离得到一类结构经表征确认的(OPy)₂Ti(OR‘)₂（7~24）化合物，证实了该探究的有效性。