Reaction of the β-diketiminato lithium salt Li(OEt 2 )[HC(CMeNAr) 2 ] (Ar ) 2,6-i-Pr 2 C 6 H 3 ) with GeCl 2 ‚(dioxane) and SnCl 2 in diethyl ether provided the monomeric complexes [HC-(CMeNAr) 2 ]MCl (M ) Ge (2), Sn (3), respectively) with a three-coordinated metal center. The reductive dehalogenation reactions of 3 with C 8 K and LiAlH 4 afforded [HC(CMeNAr) 2 ] 2 Sn (7) and [HC(CMeNAr) 2 ]AlH 2 , respectively. The metathesis reactions of 3 with t-BuLi, AgSO 3 -CF 3 , and NaN 3 resulted in the formation of [HC(CMeNAr) 2 ]Sn(t-Bu) (4), [HC(CMeNAr) 2 ]-Sn(OSO 2 CF 3 ) (5), and [HC(CMeNAr) 2 ]SnN 3 (6), respectively. Compounds 2, 3, 5, and 7 were characterized by single-crystal X-ray structural analysis. The structures indicate that the β-diketiminato backbone is essentially planar and the metal centers reside in distortedtetrahedral environments with one vertex occupied by a lone pair of electrons. The bond angles at the metal center are in the range 85.2(8)-106.8(2)°, and the most acute angle is associated with the bite of the chelating ligand.

Treatment of [{HC(CMeNAr) 2 }GeCl] (Ar ) 2,6-iPr 2 C 6 H 3 (1), 2,6-Me 2 C 6 H 3 (2)) with Me 3 -SnF in dichloromethane at room temperature afforded the corresponding fluoride [{HC-(CMeNAr) 2 }GeF] (Ar ) 2,6-iPr 2 C 6 H 3 (3), 2,6-Me 2 C 6 H 3 (4)), while with NaBH 4 in THF under reflux for 12 h gave the hydride [{HC(CMeNAr) 2 }GeH(BH 3 )] (Ar ) 2,6-iPr 2 C 6 H 3 ( 5), 2,6-Me 2 C 6 H 3 ( 6)). Reaction of 3 with Me 3 SiN 3 in toluene provided [{HC(CMeNAr) 2 }Ge(F)NSiMe 3 ] (Ar ) 2,6-iPr 2 C 6 H 3 ( 7)). The BH 3 in 5 can be removed with Me 3 P to afford [{HC(CMeNAr) 2 }-GeH] (Ar ) 2,6-iPr 2 C 6 H 3 (8)). Treatment of 5 with tBuLi in diethyl ether led to [{HC(C(CH 2 )-NAr)CMeNAr}Ge(H)BH 3 ]Li(Et 2 O) 3 (Ar ) 2,6-iPr 2 C 6 H 3 (9)), in which a hydrogen of one of the Me groups was eliminated, and this consequently resulted in the formation of a methylene group. Compounds 3-6 are the first examples of structurally characterized germanium(II) fluorides and hydrides. Single-crystal X-ray structural analyses indicate that compounds 3, 5, and 9 are monomeric and the germanium center resides in a trigonal-pyramidal environment in 3 and in distorted-tetrahedral environments in 5 and 9. † Dedicated to Professor Max Herberhold on the occasion of his 65th birthday.

A systematic theoretical study is carried out on the mechanism for Pd(II)-catalyzed oxidative cross-coupling between electron-deficient arenes and alkenes. Two types of reaction pathways involving either a sequence of initial arene C-H activation followed by alkene activation, or the reverse sequence of initial alkene C-H activation followed by arene activation are evaluated. Several types of C-H activation mechanisms are discussed including oxidative addition, σ-bond metathesis, concerted metalation/deprotonation, and Heck-type alkene insertion. It is proposed that the most favored reaction pathway should involve an initial concerted metalation/deprotonation step for arene C-H activation by (L)Pd(OAc)(2) (L denotes pyridine type ancillary ligand) to generate a (L)(HOAc)Pd(II)-aryl intermediate, followed by substitution of the ancillary pyridine ligand by alkene substrate and direct insertion of alkene double bond into Pd(II)-aryl bond. The rate- and regio-determining step of the catalytic cycle is concerted metalation/deprotonation of arene C-H bond featuring a six-membered ring transition state. Other mechanism alternatives possess much higher activation barriers, and thus are kinetically less competitive. Possible competing homocoupling pathways have also been shown to be kinetically unfavorable. On the basis of the proposed reaction pathway, the regioselectivity predicted for a number of monosubstituted benzenes is in excellent agreement with experimental observations, thus, lending further support for our proposed mechanism. Additionally, the origins of the regioselectivity of C-H bond activation is elucidated to be caused by a major steric repulsion effect of the ancillary pyridine type ligand with ligands on palladium center and a minor electronic effect of the preinstalled substituent on the benzene ring on the cleaving C-H bond. This would finally lead to the formation of a mixture of meta and para C-H activation products with meta products dominating while no ortho products were detected. Finally, the multiple roles of the ancillary pyridine type ligand have been discussed. These insights are valuable for our understanding and further development of more efficient and selective transition metal-catalyzed oxidative C-H/C-H coupling reactions.

Aims: To isolate and identify nitrogen-fixing bacilli from the plant rhizospheres in Beijing region of China. Methods and Results: A total of 29 isolates were selectively obtained from the rhizospheres of wheat, maize, ryegrass and willow based on their growth on nitrogen-free medium and their resistance to 100°C for 10 min. Of the 29 isolates, seven had nifH gene determined by PCR amplification. The seven isolates were found to belong to the genera Bacillus and Paenibacillus based on phenotypic characterization, 16S rDNA sequence, G+C content and DNA-DNA hybridization. Isolates T1 and W5 were identified as Bacillus cereus and Bacillus marisflavi respectively. Isolates G1, C4 and C5 were identified as Bacillus megaterium. Isolate G2 was identified as Paenibacillus polymyxa and isolate T7 as Paenibacillus massiliensis. Conclusions: This study suggests that nifH gene could be detected in the both genera Bacillus and Paenibacillus. These degenerate primers for nifH gene fragment used in this study were shown to be useful for identifying nitrogen-fixing bacilli. Significance and Impact of the Study: It is the first demonstration that nitrogen fixation exists in B. marisflavi and P. massiliensis and the first report of the sequences of the nifH gene from B. megaterium and B. cereus. The nitrogen-fixing bacilli obtained in this study will be used in our future research for investigating the mechanisms of nitrogen fixation in bacilli.

Reaction of [HC(CMeNAr)2]GeCl (Ar = 2,6-iPr2C6H3) with RLi (R = Me, nBu) in diethyl ether at −78 °C yielded the alkylgermanium(II) compounds [HC(CMeNAr)2]GeR (R = Me (5), nBu (6)), which are monomeric with a three-coordinate germanium center. Compound 5 was oxidized with sulfur and selenium to afford [HC(CMeNAr)2]GeMe(E) (E = S (7), Se (8)), in which a terminal GeE double bond is present. Treatment of 5 with trimethylsilyl azide in hexane at room temperature gave [HC(C(CH2)NAr)CMeNAr]GeMe(N(H)SiMe3) (9), containing a Ge−N single bond; the expected compound [HC(CMeNAr)2]GeMe(NSiMe3) with a GeN double bond was not observed. The latter reaction proceeds with migration of a hydrogen atom from a methyl group of the ligand backbone to the nitrogen atom bonded to the silicon atom with formation of a methylene moiety. X-ray structural data are provided for 5, 6, 8, and 9.