Syntheses of Molybdenum Oxo Benzylidene Complexes

The reaction between
Mo­(O)­(CHAro)­(ORF6)2(PMe3) (Aro = ortho-methoxy­phenyl,
ORF6 = OCMe­(CF3)2) and 2 equiv of
LiOHMT (OHMT = O-2,6-(2,4,6-Me3C6H2)2­C6H3) leads to Mo­(O)­(CHAro)­(OHMT)2, an X-ray structure
of which shows it to be a trigonal bipyramidal anti benzylidene complex in which the o-methoxy oxygen
is coordinated to the metal trans to the apical oxo
ligand. Addition of 1 equiv of water (in THF) to the benzylidyne complex,
Mo­(CArp)­(OR)3(THF)2 (Arp = para-methoxyphenyl, OR = ORF6 or OC­(CF3)3 (ORF9)) leads to formation of {Mo­(CArp)­(OR)2­(μ-OH)­(THF)}2­(μ-THF)
complexes. Addition of 1 equiv of a phosphine (L) to Mo­(CArp)­(ORF9)3(THF)2 in THF, followed
by addition of 1 equiv of water, all at room temperature, yields Mo­(O)­(CHArp)­(ORF9)2(L) complexes in good
yields for several phosphines (e.g., PMe2Ph (69% by NMR),
PMePh2 (59%), PEt3 (69%), or P­(i-Pr)3 (65%)). The reaction between Mo­(O)­(CHArp)­(ORF9)2(PEt3) and 2 equiv
of LiOHMT proceeds smoothly at 90 °C in toluene to give Mo­(O)­(CHArp)­(OHMT)2, a four-coordinate syn alkylidene complex. Mo­(O)­(CHArp)­(OHMT)2 reacts with ethylene (1 atm in C6D6) to give
(in solution) a mixture of Mo­(O)­(CHArp)­(OHMT)2, Mo­(O)­(CH2)­(OHMT)2, and an unsubstituted
square pyramidal metallacyclobutane complex, Mo­(O)­(CH2CH2CH2)­(OHMT)2, along with
ethylene and ArpCHCH2. Mo­(O)­(CHArp)­(OHMT)2 also reacts with 2,3-dicarbo­methoxy­norbornadiene
to yield syn and anti isomers of
the “first-insertion” products that contain a cis CC bond.

配合物Mo(O)(CHAro)(ORF6)₂(PMe₃) [其中PMe₃为三甲基膦（trimethylphosphine），Aro为邻甲氧基苯基（ortho-methoxyphenyl），ORF6为OCMe(CF₃)₂] 与2当量的LiOHMT [OHMT为O-2,6-二(2,4,6-三甲基苯基)苯氧基（O-2,6-bis(2,4,6-trimethylphenyl)phenyl）] 发生反应，生成Mo(O)(CHAro)(OHMT)₂。经X射线晶体结构表征，该产物为三角双锥构型的反式亚苄基配合物，其中邻甲氧基的氧原子与金属中心配位，且该配位位点处于与轴向氧配体反式的位置。向苄基卡拜配合物Mo(CArp)(OR)₃(THF)₂ [其中THF为四氢呋喃（tetrahydrofuran），Arp为对甲氧基苯基（para-methoxyphenyl），OR为ORF6或OC(CF₃)₃（ORF9为三(三氟甲基)甲氧基（tris(trifluoromethyl)methoxy））] 中加入1当量的水（溶于四氢呋喃中），可形成{Mo(CArp)(OR)₂(μ-OH)(THF)}₂(μ-THF)类配合物。在四氢呋喃溶剂中，向Mo(CArp)(ORF9)₃(THF)₂中加入1当量的膦配体（L），随后于室温下再加入1当量的水，可得到一系列Mo(O)(CHArp)(ORF9)₂(L)型配合物，多数膦配体参与的反应收率良好：例如二甲基苯基膦（PMe₂Ph，核磁共振波谱（NMR）定量收率69%）、甲基二苯基膦（PMePh₂，59%）、三乙基膦（PEt₃，69%）以及三异丙基膦（P(i-Pr)₃，65%）。配合物Mo(O)(CHArp)(ORF9)₂(PEt₃)与2当量的LiOHMT在甲苯（toluene）中于90℃下平稳反应，生成四配位的顺式亚烷基配合物Mo(O)(CHArp)(OHMT)₂。Mo(O)(CHArp)(OHMT)₂可与乙烯（氘代苯C₆D₆中1大气压条件下）反应，溶液中得到混合产物：未反应的Mo(O)(CHArp)(OHMT)₂、亚甲基钼配合物Mo(O)(CH₂)(OHMT)₂，以及未取代的四方锥构型金属环丁烷配合物Mo(O)(CH₂CH₂CH₂)(OHMT)₂，同时伴随乙烯与ArpCH=CH₂的生成。Mo(O)(CHArp)(OHMT)₂亦可与2,3-二甲氧羰基降冰片二烯反应，生成含有顺式碳碳双键的“首次插入”产物的顺式与反式异构体。