Most of the applications of phthalocyanines (Pcs) are concerned with the large, flat π-conjugation system, as well as the type of central metal. 1 In particular, it is well-known that, compared with porphyrins, 2 the metalloPcs (MtPcs) have extremely high planarity: for example, nonsubstituted NiPc is essentially perfectly planar, 3 although MtPcs with larger metal ions such as Pb and Sn distort the geometry to some extent. 4 Structurally distorted Pcs have been reported in the past few years, where the steric congestion of substituents caused distortion of the macrocycle. 4,5 In this communication, we report two types of Pc analogues whose nonplanarity appears to be the highest yet reported. To induce the largest distortion conceivable, aromatic ortho-dinitriles having two protruding phenyl groups, 3 and 4, are used. These types of dinitriles have long been believed to be too congested to form Pcs by themselves 6 and have therefore been employed for the preparation of opposite type of MtPc analogues, utilyzing the steric hindrance between the phenyl groups. 7 In the course of studies, however, we thought that, if these dinitriles can occupy the adjacent positions of Pcs, the deviation from planarity would be very large because of the overlap of the protruding phenyl groups. 8 As described below, we have overcome this problem, and the resultant two Pc analogues obtained by the above inverse concept, 1 and 2, are indeed confirmed to be the most nonplanar Pcs ever substantiated structurally.Both 1 9 and 2 10 were prepared by the so-called lithium method 1 at ca. 170 and 150 °C, respectively (Scheme 1). In the case of 2, dinitriles 4 and 5 were co-macrocyclized, so that repeated chromatography was inevitably required. They were characterized using mass spectra, elemental analysis, and 1 H NMR (only for 1) 9,10 and their molecular structures were analyzed by X-ray crystallography. Crystals were grown in either chloroform-hexane (1) or acetone-containing toluene (2).
Considerable attention has been focused on the synthesis and chemical behavior of silylene-transition metal complexes. 1,2 Silyl(silylene) complexes L n M(dSiR 2 )-SiR 3 are one of the attractive synthetic targets since such complexes have been assumed to be key intermediates in many transition metal-catalyzed scrambling of substituents and skeletal redistribution of organosilicon and organosilicon-transition metal compounds. 2,3 Silyl-(silylene) complexes have been isolated as internal or external donor-stabilized complexes in which the electrondeficient silylene ligands are stabilized by coordination of two-electron donors. 4-7 Lappert et al. very recently reported the synthesis of the first donor-free silyl-(silylene) complex by the reaction of an isolable silylene and a platinum complex. 8 The silylene ligand in this complex is stabilized electronically by delocalization of lone pair electrons of two amino substituents attached to the silicon atom. There has been no base-free silyl-(silylene) complexes with only alkyl or aryl groups on the silicon atoms.In our previous work on donor-stabilized silyl(silylene) 6,7 and donor-free germyl(germylene)tungsten complexes, 9 we found that the tungsten fragment Cp′W(CO) 2 (Cp′ ) η-C 5 Me 5 , η-C 5 H 5 ) stabilizes the R 3 E-MdER 2 framework efficiently (E ) Si, Ge; M ) metal fragment). This prompted us to synthesize basefree silyl(silylene)tungsten complexes. Here we report the photolysis of a methyltungsten complex in the presence of hydrodisilanes. This reaction afforded either a monomeric base-free silyl(silylene)tungsten complex or a self-stabilized dimer of a silyl(silylene)tungsten complex depending on the sustituents on the silicon atoms.Photolysis of Cp′W(CO) 3 Me (1a, Cp′ ) Cp*, Cp* ) η-C 5 Me 5 ; 1b, Cp′ ) η-C 5 Me 4 Et) in the presence of excess HSiMe 2 SiMe 3 in hexane afforded yellow crystals of a self-stabilized silyl(silylene)tungsten complex with a dimeric structure, [Cp′W(CO) 2 (dSiMe 2 )(SiMe 3 )] 2 (2a, Cp′ ) Cp*; 2b, Cp′ ) η-C 5 Me 4 Et) in 87 and 54% yield, respectively (eq 1). Crystal structure analysis confirmed that complex 2b is the first silylene complex stabilized by coordination of an isocarbonyl ligand, which is coordinated to a tungsten fragment and a silylene ligand via its carbon and oxygen atom, respectively (Figure 1). The tungsten-silylene bond (W-Si(2) 2.489(2) Å) is significantly shorter than the tungsten-silyl bond (WSi(1) 2.609(2) Å), indicating partial double bond character for the W-Si (2) bonding. The silylene ligand is † Present address: Tobita, H.; Shimoi, M.; Ogino, H. J. Am. Chem. Soc. 1988, 110, 4092. (b) Tobita, H.; Ueno, K.; Shimoi, M.; Ogino, H.
The formation and high reactivity of transition-metal-element multiple bonds plays an important role in transitionmetal-catalyzed reactions, in particular, by facilitating the cleavage and formation of usually robust bonds. Olefin metathesis is a typical and very useful example of this type of reaction, in which carbene complexes, which have a metalcarbon double bond, are not only key intermediates but may also act as high-performance catalysts.[1] In contrast to metal-carbon multiple bonds, metal-element multiple bonds, where the element is from the third or subsequent row of the periodic table, have been much less widely investigated. Among them, silylene complexes, which possess a metal-silicon double bond, have been the most extensively studied, [2][3][4][5][6][7][8][9] but the mechanisms of their reactions remain rather unclear.Both ourselves and Pannell's group have insisted, through the generation of silyl(silylene) complexes with transition metals from groups 6 to 9 and the preparation of their donorstabilized forms, that 1,2-and 1,3-group migrations of these systems (Scheme 1) occur very easily under mild conditions, and cause the metal-catalyzed oligomerization/deoligomerization, isomerization, and redistribution of organosilicon Scheme 1. Illustrating the 1,2-and 1,3-group migrations in silyl(silylene) complexes with metals of groups 6 to 9.
Donor-stabilized bis(silylene)tungsten complexes CpW(CO) 2 {(SiMe 2 )‚‚‚Do‚‚‚(SiMe 2 )} (Cp ) η-C 5 H 5 ; Do ) NEt 2 (1), OMe (2)) were synthesized by photolysis of a C 6 D 6 solution containing CpW(CO) 3 Me and HSiMe 2 SiMe 2 Do. The X-ray crystal structures of 1 and 2 revealed that the W-Si bonds (2.502(2) and 2.501(2) Å for 1; 2.490(3) Å for 2) are significantly shorter than those of structurally similar silyltungsten complexes, while the Si-N bonds (1.930(6) and 1.920(7) Å) in 1 and the Si-O bonds (1.792(7) Å) in 2 are much longer than usual Si-N and Si-O single bonds. These structural data indicate that the W-Si bonds bear partial double bond character, whereas the Si-N and Si-O bonds are regarded as a hybrid of covalent bonding and dative bonding. The unsaturated nature of the tungstensilicon bonds is also indicated by the significant downfield shift of the 29 Si NMR signals as well as large coupling constants between 29 Si and 183 W (1 δ ) 62.1 ppm, 1 J W-Si ) 91.5 Hz; 2 δ ) 99.3 ppm, 1 J W-Si ) 99.3 Hz) compared to those of structurally similar silyltungsten complexes. The tungsten complexes 1 and 2 showed fluxional behavior due to silylenemethyl group exchange and, in the case of 1, N-Et group exchange. A mechanism containing the generation of a base-free silyl(silylene)tungsten complex as the key intermediate is proposed for the fluxional process.
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