Heterocyclopentadienyl Complexes of Group-3 Metals

Phosphorus Heterocycles

“…By far the most important phospholyl complexes are the g 5 species (M). They are known for almost all of the transition metals of the periodic table, including rare earths [83] and uranium [84]. Most of them are 18e species but, recently, a 16e phosphachromocene [85], a 17e phosphaferricinium [86], a 19e phosphacobaltocene [87] and a 20e phosphanickelocene [88] have been described.…”

Bis(μ-5-diisopropylamino-1,2,3,4-tetrazolido-κ2N2:N3)bis[(triisopropylphosphane)copper(I)]

“…The coordination chemistry of anionic five-membered nitrogen heterocyclic ligands has generated considerable recent interest from several different perspectives (Nief 2001, Rottger et al 1994, Hitzbleck et al 2004, Gust et al 2001, Dezelah et al 2004, Sebe et al 2005, Gust et al 2002, Vela et al 2006. Due to the presence of many nitrogen atoms in 1,2,4-triazolato and tetrazolato ligands, complexes containing these ligands have a strong tendency to form oligomeric and polymeric compounds through bridging ligand coordination modes (Haasnoot 2000, Zhang et al 2006, Dinca et al 2006).…”

f‐Block Phospholyl and Arsolyl Chemistry

“…Given the huge influence of substituents in f‐block Cp R chemistry, the comparative dearth of examples of isoelectronic heterocyclopentadienyl f‐block complexes, where one or more of the ring C atoms is substituted by other p‐block atoms, is noteworthy [8] . Of these related ligand families, phospholyls (C 5− n R 5− n P n ) and arsolyls (C 5− n R 5− n As n ) have proved popular, with the lighter congeners more widely investigated, and their group 3 and f‐block metal chemistry was reviewed several times between 1998 and 2006 [3a, 8, 9] . The relatively restricted development of f‐block phospholyl and arsolyl chemistry compared with that of Cp and Cp R analogues is mirrored in the s‐, p‐ and d‐blocks [9a, b] .…”

“…The reasons for this disparity are the same as for other heterocyclopentadienyls: the well‐documented benefits of Cp and Cp R ligands summarised above, together with their widespread renown, make them natural primary choices for chemists in exploratory synthesis fields [2a, b] . However, for more nuanced and specific applications, the introduction of ring heteroatoms can provide electronic fine‐tuning to maximise physicochemical properties, providing rich and diverse chemistry [8] …”

“…The relative popularity of phospholyls and arsolyls in f‐block chemistry compared with other heterocyclopentadienyls can be attributed to both pragmatic (i–ii) and ligand design (iii–vi) considerations: [3, 8, 9] (i) synthetic routes to monophospholyls and ‐arsolyls are mature and are relatively straightforward; (ii) 31 P nuclei are I =1/2 with 100 % natural abundance ( 75 As I =3/2, 100 % abundant), providing a useful NMR/EPR spectroscopic handle; (iii) phospholyl and arsolyl ligands are relatively soft compared with Cp R analogues and are thus well‐suited for stabilising low oxidation state f‐block ions; (iv) phospholyls and arsolyls are able to bind in a η 1 ‐fashion through their P/As lone pairs but are more likely to exhibit an η 5 ‐binding mode than lighter congeners with harder heteroatom donor atoms, for example, pyrrolyl (C 4 R 4 N) and pyrazolyl/imidazolyl (C 3 R 3 N 2 ), thus they more effectively mimic Cp R ligands in occupying a large proportion of metal coordination spheres; (v) the P and As lone pairs provide a range of alternative binding modes over Cp R ; for example, for monophospholyls μ:η 5 ,η 1 ‐ and μ:η 1 ‐binding modes increase the likelihood of formation of multinuclear complexes; and, (vi) phospholyls and arsolyls are poorer π‐donors and stronger π‐acceptors than analogous Cp R ligands, influencing metal reduction potentials and redox chemistry.…”