ANSWERS TO EXERCISES REFERENCES ABBREVIATIONS INDEX ATOMIC WEIGHTS OF THE ELEMENTS PERIODIC TABLE OF THE ELEMENTS ANSWERS TO EXERCISES CHAPTER 1 + + 1.1. [FeCp2] , sandwich structure with parallel rings, [FeL4X2] , 17, 5, 3, 6; [RhCl(PPh3)3], square planar, [RhL3X], 16, 8, 1, 4; [Ta(CH2CMe3)3(CHCMe3)], tetrahedral, [TaX5], 10, 0, 5, 4; [ScCp*2(CH3)], bent sandwich with CH3 in the equatorial plane, [ScL4X3], 14, 0, 3, 7; [HfCp2Cl2], bent sandwich with both Cl ligands in the equatorial plane, [HfL4X4], 16, 0, 4, 8; – – [W(H)(CO)5] , octahedral, [WL5X] , 18, 6, 0, 6; 2 2+ 2+ [Os(NH3)5( -C6H6)] , octahedral, [OsL6] , 18, 6, 2, 6; [Ir(CO)(PPh3)2(Cl)], square planar, [IrL3X], 16, 8, 1, 4; [ReCp(O)3], pseudo-octahedral, [ReL2X7], 18, 0, 7, 6; 2– 2– [PtCl4] , square planar, [PtX4] , 16, 8, 2, 4; – – [PtCl3(C2H4)] , square planar, [PtLX3] , 16, 8, 2, 4; [CoCp2], sandwich structure with parallel rings, [CoL4X2], 19, 7, 2, 6; 6 [Fe( -C6Me6)2], sandwich structure with parallel rings, [FeL6], 20, 8, 0, 6; [AuCl(PPh3)], linear, [AuLX], 14, 10, 1, 2; 4 [Fe( -C8H8)(CO)3], trigonal bipyramid (piano stool), [FeL5], 18, 8, 0, 5; 1 2+ 2+ [Ru(NH3)5( -C5H5N)] , octahedral, [RuL6] , 18, 6, 2, 6; 2 + + [Re(CO)4( -phen)] , octahedral, [(ReL6] , 18, 6, 1, 6; + + [FeCp*(CO)(PPh3)(CH2)] , pseudo-octahedral (piano stool), [(FeL4X3] , 18, 6, 4, 6; 2+ 2+ [Ru(bpy)3] , pseudo-octahedral, [RuL6] , 18, 6, 2, 6. 2 1.2. In the form [FeCp*( -dtc)2], both dithiocarbamate ligands are chelated to iron, 2 1 [FeL4X3], 19, 5, 3, 7. In the form [FeCp*( -dtc)( -dtc)], one of the two dithio- carbamate ligands is chelated to iron whereas the other is monodentate, [FeL3X3], 17, 5, 3, 6. The two forms having respectively 19 and 17electrons are both to some extent destabilized, being both one electron away (in excess and shortage respectively) with respect to the robust 18-electron structure. The main reaction of 19-electron complexes in the absence of other substrate is to partially decoordinate giving a 17-electron complex, and this reaction is very fast. The main reaction of 17-electron complexes in the presence of a ligandL (in the absence of reducing agent) is also very fast, addition giving the 19-electron complex. Thus, the 536 OGANOMETALLIC CHEMISTRY AND CATALYSIS dissociation of 19-electron complexes and re-association of the 17-electron complex formed with the dissociated ligand make a rapid equilibrium between these two species that only ends up by the reaction of either form, if any. 1.3. It is known that O2 can coordinate to a transition metal in a side-on mode (as ethylene does), which is the case in this complex, or end-on (with an angle) as in hemoglobin and myoglobin. In the case of the side-on coordination, the ligand is an Lligand if the metal is electron poor, the length of the double O=O bond being relatively little changed by the coordination. If, on the other hand, the metal center has a high electron density, as inthis case, the O2ligand undergoes an oxidative addition leading to the lengthening of the O-O bond that can, at the limit, reach the length of a single O-O bond. The metal-O2 species should then be formally III described as an Ir metallocycle, the O2ligand now being a peroxo X2ligand in the Ir-O2 triangle structure. + 1.4. [CoCp2] : organometallic 18-electron, thus stable complex. – [CoCp2] : 20-electron organometallic sandwich complex (triplet state, having two unpaired electrons with the same spin) isoelectronic to nickelocene (a commercial compound). The stabilities of these two complexes are weakened by the double occupancy of the doubly degenerate antibonding orbital (two orbitals having the same energy are occupied by two electrons). The orbital energy level is not too high, however, in spite of its antibonding character, which allows the isolation and crystallization of these two reactive complexes. + [V(CO)7] : the addition of two disadvantages, a coordination number larger than 6 and the cationic nature of a binary metal carbonyl leads to the non-inexistence of this complex in spite of its 18-electron structure. [Cr(H2O)6]: non-existent as all the binary water complexes in which the metal has a low oxidation state such as (0). 2+ – [Ni(H2O)6] : relatively stable 20-electrons complex as [CoCp2] , vide supra, and in addition because of the ideal coordination number (6) and oxidation state (II). 2– [ReH9] : stable 18-electron complex in spite of its very high coordination number, because hydrides, the only ligands present in the coordination sphere, are very small. [Zr(CH2Ph)4]: in principle an 8-electron complex that is thermodynamically stable but kinetically very reactive with many substrates. The stability, in spite of the very low NVE, is due partly to the absence of H, and partly to the interactions between the phenyl rings and the metal decreasing the Zr-C-Ph angle below 109° (the value of the NVE=8, only is conventional and does not take this interactions into account). [Zr(CH2Ph)4(CO)2]: does not exist as almost all the mono- and bimetallic metal-car- bonyl structures in which the metals do not have non-bonding electrons (NNBE=0) (the M-CO bond needs backbonding from some filled metal dorbitals). There are only exceptions in lanthanide chemistry in which the metal-CO bond is very weak (R. Anderson’s work). ANSWERS TO EXERCISES 537 2– [Cr(CO)5] : stable 18-electron complex as all the binary mono- or polyelectronic metal-carbonyl 18-electron complexes in which the metal is at the 0, –1 or –2 oxida- tion state. [Cu(Cl)(PPh3)]: stable; Cu, Ag and Au commonly gives complexes having the MLX 14-electron structure; [Ir(CO)2(PPh3)(Cl)], [Pt(PPh3)3]: 16-electron complexes of noble metals of groups 9 and 10 respectively, very stable as usually the group 8-10 noble metal 16-electron complexes are if the oxidation state is also adequate. [ScCp*2(CH3)]: stable (but reactive) 14-electron complex (classic structure also with the lanthanides, these complexes being initiators of olefin polymerization) [NbCp2(CH3)3]: stable (but reactive) 18-electron organometallic complex. + [FeCp*(dtc)2] : stable 18-electron complex in spite of its odd coordination number (7), because the high oxidation state (IV) is ideal in a mixed inorganic- organometallic complex with dominant inorganic components. 1.5. The optimal stability of this type of complex corresponds to a NVE=18, the number of electrons provided by the ambivalent, versatile ligand Ph2C2 is 4 for two of them and 2 for the 3rd one. 1.6. The order of decreasing thermal stability of these metallocenes is dictated by the 18-electron rule (NEV): [FeCp2] (18e)>[MnCp2] (17e) and [CoCp2] (19e)>[CrCp2] (16e) and [NiCp2] (20e)>[VCp2] (15e)>[TiCp2] (14e). 1.7. The splitting of these 5dorbitals into 3degenerate bonding levels (of identical energy) t2g and 2degenerate antibonding eg levels is represented page40. Manganese has 5delectrons, one in each orbital (the semi-filling of these 5orbitals stabilizes this electronic structure). The total spinS is 5/2 (high-spin structure, 1/2 multiplicity 2S+1: sextuplet state). μtheor.=[5(5+2)] =5.916μB. With Cp*, the 5electron-releasing methyl substituents strengthen the ligand field, forcing the 1/2 electrons to pair in a low-spin state S=1/2 (doublet state: μtheor.=[1(1+2)] =1.732μB). 1.8. The electronic density on manganese increases as the acceptor character of the ligands decreases: CO<CS<C2H4<THF<PPh3. Detection by infrared spectros- copy or cyclic voltammetry: the absorption frequency of the carbonyls and the oxi- dation potential of the complex decrease as the electronic density increases. It is the complex [MnCp(CO)2L], L=CO, that is the most difficult to oxidize in this series. 1.9. Bent sandwich complex, the two carbonyls being in the equatorial plane. The two rings are connected by a dimethylene bridge that hinders the free rotation. One of the Cp’s is pentahapto, whereas the other Cp has to be trihapto in order to obey the 18-electron rule. 538 OGANOMETALLIC CHEMISTRY AND CATALYSIS CHAPTER 2 2.1. CO O OC C CO CO Fe Fe Cr Cr OC C OC CO O OC CH2Ph CO CO OC S CO WW Rh Rh S Ph3P CO OC CO OC Ph P CO OC 3 CH2Ph [FeCp(CO)(μ-CO)]2: [FeL4X2], 18, 6, 6; [CrCp(CO)3]2: [CrL5X2], 18, 4, 7; [W(CO)4(μ2-SCH2Ph)]2: [WL5X2], 18, 4, 7; 5 5 {[Rh(CO)(PPh3)]2( , ,μ2-fulvalenyl)}: [RhL4X], 18, 8, 5. 2.2. 2, 3, 2. 2.3. [Re4H4(CO)12]: NEC=56 (localized count: counting, to simplify, H as bridging 1electron; 17 on each Re, i.e. 68 for 4 Re, minus 12 for the 6 Re-Re bonds of the Re4 tetrahedron); 2– {Fe6[C(CO)16]} : NEC=86. For the localized count, one can attribute 3 CO’s for each of the 4 equatorial Fe’s and 2 for the 2 apical Fe’s that are formally bridged by the Cligand that is doubly bonded to each of the two Fe’s. This gives 18 for each Fe, but the 2electrons of the negative charges make too many for a localized count with 18electrons per Fe. This count gives (618)+2=110 less the 24 of the 12 formal Fe-Fe bonds of the octahedron. [NiCp]6: NEC=90. For the localized count, one has 6 NiL2X5, i.e. 6 19=114 less the 24 of the 12 formal Ni-Ni bonds of the Ni6 octahedron.