CI32I C133) F i g . 4 . 2 . 5 T h e m o l e c u l a r s t r u c t u r e o f [ S m ( T p ^ ' ’''^')2] [ T e3P h3] , 4 f , C (4 6 ) C (4 7 ) C (4 5 ) C (4 8 ) T e ( 2 ) T e ( 3 ) C (3 3 ) C(31) C (34) C (3 8 ) C (3 5 ) C (4 2 ) C I39) C(41) C (4 0 )
Fig. 4.2.6 T h e stru ctu re o f [T e3? h3]' anion
[Sm (Tp'^‘^’^ ‘^)2][T e3P h3]. The leakage o f small am ounts o f air into the flask during crystallization m ight result in the oxidative coupling o f the TePh anion to diphenylditelluride. A ddition o f TePh to the PhTeTePh w ould then give the corresponding trinuclear anion. One m ight then expect the larger [Te3Ph3]“ anion to give a less soluble salt w ith {Sm(Tp^®’^ ‘^)2}^ than [TePh]" as a result o f the better size m atch, and therefore to crystallize m ore easily from the solution.
4.2.7 Preparations of
and Sm(Tp"""’^02(SePh''®“)
The preparations o f the selenolate complexes were carried out in an analogous m anner to those for the thiophenolate com plexes (Eq. 4.2.12).
(Eq. 4.2.12) 2 [Sm (Tp^"’% ] + (S e P h ^ - ° % > 2 [Sm (Tp^"’% S e P h ^ - ° ^ T
T h e lR spectrum o f each product showed a peak near 2560 cm’’ which w as assigned to the usual B-H stretch. The N M R spectrum showed three broad peaks in the ratio o f 3:3:1 assigned to the tris(pyrazolyl)borate ligands, together w ith appropriate peaks for the protons on the selenolate ligand.
The high solubilities o f these two complexes in non-polar solvents seem to indicate m olecular structure. U nfortunately num erous attempts to obtain crystals suitable for X -ray crystallography failed, and pow ders were obtained in each case. Further efforts to crystallize these m aterials are currently being made by Miss. A. C. Hillier.
4.3 Preparation o f bimetallic lanthanide-transition metal complexes
4.3.1 Introduction
In order to explore further the steric definition provided by (T p'^°’^ ‘^)2 ligand set, we began to examine the reactions o f samarium (11) w ith transition metal carbonyl com pounds containing metal-metal single bonds. There is considerable current interest in
heterobim etallic complexes due to the search for homogenous counterparts o f Fischer- T rop sch catalysts^^ and because o f the possibility o f isolating com pounds containing direct M -L n interactions. M ost o f the reported transition metal-lanthanide heterobimetallic com plexes are those linked via isocarbonyl bridges, i.e. they contain M -CO -Ln unit (M = transition metal). Reactions o f this type are w ell-precedented with metallocene com pounds. Thus the reaction o f [Yb(ri^-C5M e5)2(O Et2)] w ith F e3(C0 ) , 2 and [Co(r|^- C -H ,)2(C0 )2] yields the structurally related clusters {[(T|^-C5Me$)2Yb]2[Fe3(C0)i ]]}^^ and {[(r|^-C5M e5)2Y b]2Co3(ri^-C5H5)2(CO )4}^^ respectively. In contrast the reactions w ith M n2(CO)io and Co2(CO)g yielded complexes o f formula [(r|^-C5M e5)2Yb(p.- O C )2M n(C O )3]2^^ and [(Ti^-C5M e5)2Y b(n-O C )C o(C O )3(THF)]^° respectively. [Sm(Ti^- C5M e5)2(TH F)2] reacts w ith Co2(CO)g to give [Sm(ri^-C5M e5)2(TH F)][C o(C O )4] and w ith [Fe(r|^-C5M e5)(C O )2]2 to give the tetranuclear complex [(ri^-C5M e5)2Sm(p,-OC)2Fe(T]^- C5M e5)]2.'^^ A fter our experimental w ork was com pleted, the complex [(THF)4l2Sm(p.- O C )M o(C O )2(ri^-C5H5)] was reported, prepared by the reaction o f Sml2 w ith
[CpM o(CO)3]2/'^ , .
A lthough direct metal-metal interactions betw een lanthanides and transition metals are considered unlikely because o f the poo r radial extension o f the valence 4 f orbitals, th e y were proposed to exist in some organom ercury ytterbium halides. Such com pounds have been prepared according to Eq. 4.3.1
(Eq. 4.3.1) Yb + R H gl > RHgYbI(THF)n
However, these have not been characterised crystallographically.
B y contrast, the binuclear complex [C p2(T H F )L uR u(C O )2(Cp)] which is prepared as show n below:
NaCl
has an unusual structure. The Lu-R u distance is 2.955 Â and the interaction is n o t supp orted by bridging carbonyl g r o u p s .B e le ts k a y a and co-w orkers have also p rep ared som e com plexes believed to contain La-Ru bonds, [(TH F)3l2L aR u(C O )2Cp] and [(T H F)(C p)L a{R u(C O )2Cp}(p,-I)2N a(T H F )2], although no structural confirm ation exists."^^
4.3.2 P r e p a r a tio n s o f [S m (T p ^ "’^ ")2(p-O C )M o(Ti^-C5H4M e )(C O )2]
The reaction o f two equivalents o f [Sm(Tp^®’^®)2] w ith [(Mo(Ti^-C5H4M e)(C O )3]2 in toluene at low tem perature resulted in the gradual dissolution o f the purple samarium starting material and gave an orange solution which, after filtration and cooling to -3 0°C , yielded analytically pure yellow to orange crystals o f [Sm(Tp'^®’^ ‘^)2(M--OC)Mo(r|^- CsH4M e)(C0 )2], 4h (Eq. 4.3.3).
(Eq. 4.3.3) 2[S m (T p ^ ''^ ')2]+[(M o(n^-M eC p)(C O )3]2 - 2[Sm (T p^"’^ ")2(!A-OC)Mo(Ti^- M eC p )(C0)2]
The crystals dissolved easily in THE and w arm toluene and decom posed in w et or chlorinated solvents. The solid state infrared spectrum show s the expected B-H stretching absorption at 2555 cm"’. Three very intense bands also appear in the carbonyl region corresponding to the stretches o f the term inal CO groups at approxim ately 1914 and 1825 cm'* and a very low energy band around 1636 cm'* w hich w e ascribe to a bridging isocarbonyl group, in a range sim ilar to those observed by previously."*^
T he *H N M R spectrum o f 4h show s three peaks for the pyrazolyl protons, consistent w ith a fluxional system. In the hopes that the param agnetic sam arium centre might enhance the chemical shift difference betw een different environm ents at low tem perature, variable tem perature *H N M R experim ents w ere carried out by M iss A. C. Hillier o f this group in
toluene-d%enzene-d*^ solution. These show ed the expected Curie-W eiss shift in the position o f the peaks due to the pyrazolyl groups."^^ Below -8 0 °C the peak due to the 3- m ethyl groups broadened into the baseline but no low -tem perature limit was reached. A nalogous observations were also made by undergraduate project student 0 . Zekria w ho prepared the corresponding Cr and W complexes.