Alexander C. Filippou

Enantioselective Synthetic Methodology to Prepare trans-Fused Bicyclo[5.3.0]decane Systems: an Approach to the Synthesis of the Pseudoguaiane Carbon Framework

Abstract An enantioselective method to prepare trans-fused bicyclo[5.3.0]decane systems is described. This methodology is based on two key reactions: a [4+3] cycloaddition reaction (to generate the seven-membered ring) and the Nicholas reaction (to insert the five-membered ring). The application of this methodology to the enantioselective synthesis of the pseudoguaiane carbon skeleton is presented. This enantioselective strategy for construction of the trans-fused bicyclo[5.3.0]decane system is versatile and could be applied to the preparation of a wide range of bioactive natural products containing that carbon framework.

TRICHLOROGERMYL COMPLEXES OF MOLYBDENUM AND TUNGSTEN BEARING CYCLOPENTADIENYL LIGANDS : SYNTHESIS, STRUCTURE AND ISOMERIZATION STUDIES

Molybdenum and tungsten trichlorogermyl complexes of the type cis -( η 5 -C 5 R 5 )M(CO) 2 (PMe 3 ) GeCl 3 ( 2b-2d ) ( ) were obtained by the stereoselective insertion reaction of GeCl 2 into the metal-chlorine bond of cis -( η 5 -C 5 R 5 )M(CO) 2 (PMe 3 )Cl ( 1b-1d ). Simultaneous thermal analysis (TG-DTA) of 2b-2d revealed an exothermic solid-state isomerization of 2b-2d to trans -( η 5 -C 5 R 5 )M(CO) 2 (PMe 3 )GeCl 3 ( 3b-3d ) and the thermoanalytical results were used to prepare the trans isomers 3b-3d in large scale. In comparison, the trichlorogermyl complex cis -CpW(CO) 2 (CNEt)GeCl 3 ( 5 ) was found to undergo an endothermic isomerization in the melt to afford a mixture of 5 and trans -CpW(CO) 2 (CNEt)GeCl 3 ( 6 ) in a 1:1.2 ratio. The complexes 2b-2d, 3b-3d and 6 were fully characterized and the solid-state structures of the isomers 2d and 3d were determined by single-crystal X-ray diffraction analyses.

The chemistry of 1,3,5-triazacyclohexane complexes, 7 synthesis and structure determination of ethyl(-1,3,5-tribenzyl-(−1,3,5-triazacyclohexane)) zinc(II)-hexafluorophosphate

Abstract Diethylzinc reacts with the hydrohexafluorophospate salt of 1,3,5-tribenzyl-1,3,5-triazacyclohexane (Bz3TAC) to give the cationic complex [(Bz3TAC)Zn(Et)](PF6). The crystal and molecular structure of the compound has been determined by X-ray diffraction. This structure agrees with the structure previously predicted by NOESY spectroscopy for the related compounds [(FBz3TAC)Zn(Et)](BF4)(FBz ue5fb p-fluorobenzyl) and [{(s-PhMeCH)3TAC}Zn(Et)]([BF4). The differences can be explained by close PF6−ue5f8Zn contact in the solid state.

Metal—carbon multiple bonds: Half-sandwich phenylcarbyne complexes of chromium—synthesis, structure, electrochemistry and reactions with PMe3

Abstract The chromium phenylcarbyne complexes (η5-C5R5)(CO)2Cr≡CPh (2a: R = H; 2b: R = Me) have been prepared and their structure, cyclic voltammetry and reactions with PMe3 are reported. The compounds 2a and 2b are obtained as red and purple thennolabile solids respectively after treatment of cis-Br(CO)2(pic)2Cr≡CPh (pic = 4-methylpyridine) (1) with NaCp (Cp ≡ C5H5) and KCp* (Cp* = C5Me5) respectively. Complex 2a adds PMe3 at the carbyne-carbon atom to give the green α-phosphoniocarhene complex Cp(CO)2Cr=C(PMe3)Ph (3), whereas 2b undergoes with PMe3 a carbyne—carbonyl coupling reaction to afford the green η2 ketenyl complex Cp* (CO)(PMe3)Cr[C(Ph) CO](4). Cyclic voltammetry studies show the phenylcarbyne complexes 2a and 2b and the carbene complex 3 to undergo a reversible one-electron oxidation in CH2Cl2 at E1/2 = 0.39 V, E1/2 = 0.20 V and E1/2 = −0.52 V respectively (potentials vs. the ferrocene/ferrocenium redox couple). In comparison, the ketenyl complex 4 is electrochemically inactive in the potential range of −1.5 to 1.0 V. The crystal structures of 2a and 3 are reported.

INSERTION OF GECL2 INTO MOLYBDENUM-HYDROGEN BONDS : A CONVENIENT ROUTE TO DICHLOROGERMYL COMPLEXES

Abstract Insertion of GeCl2 into the molybdenum-hydrogen bond of CpMo(CO)3H(1) affords the dichlorogermyl complex CpMo(CO)3GeCl2H(2). Complex 2 reacts with PMe3 to give trans-CpMo(CO)2(PMe3)GeCl2H (5). The mechanism of this ligand exchange reaction involving GeCl2 extrusion and insertion steps is described. Insertion of GeCl2 into the molybdenum—hydrogen bond of cis/trans-CpMo(CO)2(PMe3)H (4) offers an alternative route to complex 5. The dichlorogermyl complexes 2 and 5 are slowly chlorinated by CH2Cl2 to give the trichlorogermyl complexes CpMo(CO)3GeCl3 (3) and trans-CpMo(CO)2(PMe3)GeCl3 (6), respectively. Chlorination of the dichlorogermyl complexes occurs also with GeCl2(dioxane) in toluene. The crystal structure of 5 is described.

Stereoselective insertion of GeCl2 into tungsten–chlorine bonds of aminomethylene and aminocarbyne complexes

Abstract Treatment of Cp*(CO) 2 Wue606CNEt 2 ( 1 ) (Cp*=η 5 -pentamethylcyclopentadienyl) with HCl affords the aminomethylene complex cis -Cp*(Cl)(CO) 2 Wue605C(H)NEt 2 ( 2 ). Complex 2 inserts stereoselectively GeCl 2 into the tungsten–chlorine bond to afford cis -Cp*(GeCl 3 )(CO) 2 Wue605C(H)NEt 2 ( 3 ). Complex 3 can also be obtained directly from 1 and GeCl 2 (diox) (diox=1,4-dioxane) in CH 2 Cl 2 . Similarly, treatment of Cp**(CO) 2 Wue606CNEt 2 ( 1a ) (Cp**=η 5 -ethyltetramethylcyclopentadienyl) with GeCl 2 (diox) in toluene affords cis -Cp**(GeCl 3 )(CO) 2 Wue605C(H)NEt 2 ( 3a ). An isomerization equilibrium is established between 3 and trans -Cp*(GeCl 3 )(CO) 2 Wue605C(H)NEt 2 ( 4 ) in the melt (208°C), which favors the trans isomer ( 3 : 4 ratio=1:6). The aminocarbyne complex cis -Cp*(Cl) 2 (CO)Wue606CNEt 2 ( 5 ) reacts with GeCl 2 (diox) to yield stereoselectively spy -5-14-Cp*(Cl)(GeCl 3 )(CO)Wue606CNEt 2 ( 6 ). Complexes 2 – 6 were fully characterized and the crystal structures of the complexes 2 , 3 , 4 and 6 are presented.

Insertion of GeCl2 into group VI transition metal-chlorine bonds: synthesis, spectroscopy and structure of molybdenum and tungsten trichlorogermyl complexes

Abstract An efficient method for the synthesis of trichlorogermyl complexes is reported involving the insertion of GeCl2 into the metal-chlorine bond of Group VI transition metal complexes bearing a cyclopentadienyl (Cp) or a pentamethylcyclopentadienyl (Cpo) ligand. This is demonstrated by the reactions of the complexes η5-C5R5)M(Co)3Cl(1a-1c)(a: R ue5fb H, M ue5fb Mo, b: R ue5fb H, M ue5fb W; c: R ue5fb Me, M ue5fb W) and cis-CpM(CO)2(L)Cl (3a, 5b) 3a: M ue5fb Mo, L ue5fb PMe3 5b: M ue5fb W, L ue5fb EtNC) with GeCl2(dioxane), which afford selectively the trichlorogermyl complexes (η5-C5R5)M(CO)3GeCl3 (2a-2c) and cis-CpM(CO)2(L)GeCl3 (cis-4a, 6b), respectively. The complex cis-CpMo(CO)2(PMe)3GeCl3 (cis-4a) isomerizes in solution and in solid-state to trans-CpMo(CO)2(PMe3)GeCl 3 (trans-4a). The GeCl2-insertion reaction offers a more convenient method for the synthesis of Group VI transition metal trichlorogermyl complexes as shown by a comparison of the synthesis of cis-Cp∗W(CO)2(EtNC)GeCl3 (6c) from cis-Cp∗W(CO)2(EtNC)Cl (5c) and GeCl2(dioxane) or from Na[Cp∗W(CO)2(EtNC)](7c) and GeCl4. The crystal structures of the trichlorogermyl complexes 2a, 2c, trans-4a and 6c are reported.

INTRAMOLECULAR CARBYNE-ISOCYANIDE COUPLING TO AN ALKYNE LIGAND AT A D4 TUNGSTEN CENTER

Oxidative decarbonylation of Cp*(CO)2W≡CNEt2 (1) with PhICl2 affords the aminocarbyne complex cis-Cp*(Cl)2(CO)W≡CNEt2 (2), which reacts with tBuNC to give the CO substitution product cis-Cp*(Cl)2(tBuNC)W≡CNEt2 (3) (Cp* = C5Me5). Complex 3 undergoes a carbyne–isocyanide coupling reaction with HCl to yield the alkyne complex Cp*(Cl)3W[η2-tBu(H)NC≡CNEt2] (4). In comparison, the reaction of cis-Cp*(Cl)2[P(OMe)3]W≡CNEt2 (5) with HCl affords the 16e carbene complex Cp*(Cl)3W=C(H)NEt2 (6) after elimination of P(OMe)3. Complex 5 was obtained from the CO ligand-exchange reaction of 2 with P(OMe)3. Treatment of 6 with tBuNC yields the cationic 18e carbene complex [Cp*(Cl)2(tBuNC)2W=C(H)NEt2]Cl (7). The mechanism of the C–C coupling reaction of 3 to give 4 is discussed and the crystal structures of 4 and 6 are described.

Aminomethylene complexes of molybdenum(IV) and tungsten(IV) bearing 1,2-dithiolato ligands

Abstract The syntheses, spectroscopic data and the structures of molybdenum(IV) and tungsten(IV) aminomethylene complexes bearing 1,2-dithiolato ligands are presented. Oxidative decarbonylation of Cp*(CO) 2 Mue606CNEt 2 ( 1a , b ) ( a : M=Mo; b : M=W; Cp*=pentamethylcyclopentadienyl) with PhICl 2 affords the aminocarbyne complexes cis -Cp*(Cl) 2 (CO)Mue606CNEt 2 ( 2a , b ), which react with the 1,2-dithiolates Na 2 (mnt)×DMF, (mnt 2− =1,2-dicyanoethene-1,2-dithiolate), Li 2 (bdt) (bdt 2− =1,2-benzenedithiolate) and Li 2 (Mebdt) (Mebdt 2− =4-methyl-1,2-benzenedithiolate) to afford the substitution products Cp*(mnt)(CO)Mue606CNEt 2 ( 3a , b ), Cp*(bdt)(CO)Mue606CNEt 2 ( 4a , b ) and Cp*(Mebdt)(CO)Wue606CNEt 2 ( 5b ), respectively. Treatment of 3b with HCl yields, after elimination of CO, the 16-electron aminomethylene complex Cp*(Cl)(mnt)Wue605C(H)NEt 2 ( 6b ). Addition of HCl to the Mue5f8C triple bond of complexes 4a , b and 5b affords the 18-electron aminomethylene complexes Cp*(Cl)(bdt)(CO)Mue605C(H)NEt 2 ( 7a , b ) and Cp*(Cl)(Mebdt)(CO)Wue605C(H)NEt 2 ( 8b ), which upon heating lose carbon monoxide to afford the 16-electron aminomethylene complexes Cp*(Cl)(bdt)Mue605C(H)NEt 2 ( 9a , b ) and Cp*(Cl)(Mebdt)Wue605C(H)NEt 2 ( 10b ), respectively. An alternative approach to 9b offers the nucleophilic substitution reaction of Cp*(Cl) 3 Wue605C(H)NEt 2 with Li 2 (bdt). Complexes 2a – 10b have been fully characterized and the crystal structures of the complexes 3b , 6b and 9b are discussed.

Trimethylphosphonium trichlorogermanate(II)

The title compound, [HPMe 3 ][GeCl 3 ], features pseudotetrahedral [HP(CH 3 ) 3 ] + and trigonal-pyramidal GeCl 3 - units that form a strongly distorted perovskite structure. The Ge II centre shows a distorted octahedral environment with three short Ge-Cl bonds [average Ge-Cl = 2.3071(9) A] and three much longer interionic Ge-Cl distances [average Ge...Cl = 4.1372 (12) A].