The reaction of trans-[Mo(N 2 ) 2 (dppe) 2 ] (1; dppe ) Ph 2 PCH 2 CH 2 PPh 2 ) with excess amounts of HCtCLi‚en (en ) H 2 NCH 2 CH 2 NH 2 ) afforded the fivecoordinate Mo(0) mono(acetylene) complex [Mo-(HCtCH)(dppe) 2 ] (2). Treatment of 2 with 2 mol of [Cp 2 Fe][BF 4 ] (Cp ) η 5 -C 5 H 5 ) in THF gave the Mo(II) acetylene complex trans-[MoF(HCtCH)(dppe) 2 ][BF 4 ], while that in THF-MeCN followed by anion metathesis with NaOTf (OTf ) OSO 2 CF 3 ) led to the formation of the metallacyclopropene complex [Mo(η 3 -CHCHPPh 2 -CH 2 CH 2 PPh 2 -C,C′,P)(MeCN) 2 (dppe)][OTf] 2 .The chemical bonding and transformation of fourelectron-donating alkyne ligands at early-transitionmetal centers have been a subject of extensive research activity. 2 A wide variety of six-coordinate d 4 metal (most typically Mo(II) and W(II)) complexes with four-electrondonating alkyne ligands have been synthesized and found to exhibit intriguing reactivities. 2,3 Four-coordinate d 6 complexes of the types ML(alkyne) 3 4-8 and ML 2 (alkyne) 2 9-11 (L ) monodentate ligand) have also been reported. In contrast, five-coordinate d 6 mono-(alkyne) complexes with the general formula ML 4 -(alkyne) have been surprisingly scarce; only a few examples, including the chromium complexes [Cr(CO) 2 -{P(OMe) 3 } 2 (RCtCPh)] (R ) Ph, H), 12 have been described in the literature. Our extensive studies on lowvalent molybdenum and tungsten complexes have demonstrated that the Mo(0) center in the complex trans-[Mo(N 2 ) 2 (dppe) 2 ] (1; dppe ) Ph 2 PCH 2 CH 2 PPh 2 ) is not only effective for the activation of dinitrogen 13,14 but

The authors have developed a new technique for preparing dental CAD/CAM composite resin blocks (CRBs): the filler press and monomer infiltration (FPMI) method. In this method, surface-treated filler is molded into a green body in which the filler particles are compressed to form an agglomeration. The green body is then infiltrated with a monomer mixture before being polymerized. It is possible to produce CRBs using this method through which densely packed nanofiller is uniformly dispersed. The greater the pressure of the filler molding, the more filler in the CRB, resulting at high pressure in a very dense CRB. A CRB obtained by applying 170 MPa of pressure contained up to 70 wt% of nano-silica filler and had a flexural strength of 200 MPa, as well. It is anticipated that CRBs obtained using the FPMI method will be useful as a dental CAD/CAM material for the fabrication of permanent crown restorations.

The anionic tungsten dinitrogen complex trans-[NBu4][W(NCS)(N2)(dppe)2] reacted with primary and secondary boranes to give the corresponding boryldiazenido complexes, among which trans-[W(NCS)(N=NBHCMe2CHMe2)(dppe)2] was structurally determined. A related boryldiazenido complex was also obtained by the reaction of trans-[W(N2)2(dppe)2] with 9-borabicyclo[3.3.1]nonyl trifluoromethanesulfonate. These reactions provide the first examples of boration of coordinated dinitrogen.

Et, Ph), has been developed, in which the tungsten dinitrogen fragment acts as a novel metallonitrogen ligand to the catalytically active titanium center. Alkylation of 1d (Cp′ ) C 5 Me 5 , L ) 1/2 Et 2 PCH 2 CH 2 PEt 2 ) with MeLi gave di-and trimethyl derivatives 2d and 3d, which were structurally characterized.Polymerization of olefins catalyzed by soluble, welldefined transition metal complexes has been one of the most attractive subjects in organometallic chemistry. 2 In particular, monocyclopentadienyl titanium catalysts containing amide, phosphinimide, and aryloxy ligands have extensively been studied, and some of them are now employed commercially. 3,4 On the other hand, some examples of olefin polymerization by using heterobimetallic complexes have been reported where bis(cyclopentadienyl)M (M ) Zr, Hf) moieties are connected to other transition metals such as Mo, 5a,b Fe, 5c,d,f Co, 5f Rh, 5e-h and Ni 5a via cyclopentadienyl or phosphido ligands. However, significant enhancement in catalytic activity has rarely been observed. 5c,d,g During our long-standing study on chemical nitrogen fixation by transition metal complexes, 6 we have recently synthesized the titanium-tungsten heterobimetallic bridging dinitrogen complexes 1a and 1b ( Figure 1) having a half-sandwich titanium fragment from the reaction of tungsten dinitrogen complexes [W(N 2 ) 2 (L) 4 ] (L ) PMe 2 Ph, 1/2 dppe; dppe ) Ph 2 PCH 2 CH 2 PPh 2 ) with CpTiCl 3 . 7 We have now found that the heterobimetallic complexes of this class are excellent catalyst precursors for copolymerization of ethylene and 1-hexene. Preliminary results are described here.Copolymerization of ethylene and 1-hexene was studied using the titanium-tungsten heterobimetallic dinitrogen complexes 1a-1g as catalyst precursors, in which several new complexes, 1c-1g, were synthesized from similar reactions. The constrained geometry catalyst [(t-BuNSiMe 2 C 5 Me 4 )TiCl 2 ] (CGC) 2 was chosen as a reference in the copolymerization because it also contains both cyclopentadienyl and nitrogen-based ligands on titanium. Table 1 summarizes the polymerization results in which Al(i-Bu) 3 and [Ph 3 C][B(C 6 F 5 ) 4 ] were used as cocatalysts. The heterobimetallic dinitrogen complex 1a showed a very high catalytic activity of 376 kg mmol (cat) -1 h -1 . The copolymers produced have relatively high molecular weights (M w ) 77 × 10 4 ) and unimodal molecular weight distribution (M w /M n ) 2.2), indicating that the copolymers were produced by a single active species. It should be noted that the catalytic activity of 1a was more than 3 times as high as that of CGC under the same conditions, although the 1-hexene content was one-third of that observed in CGC.Complexes 1c-1e with depe (Et 2 PCH 2 CH 2 PEt 2 ) ligands also exhibited high catalytic activity. Complex (1) Preparation and Properties of Molybdenum and Tungsten Dinitrogen Complexes. Part 72. Part 71: Arita, C.; Seino, H.; Mizobe, Y.; Hidai, M. Nabika, M.; Imai, A.; Miyashita, A.; Watanabe, T.; Johohji, H.; Oda, Y.; Hanaoka, H. ...