Formation and Structures of Cationic Pyrazole and Pyrazolyl Zirconocene Complexes

Another Surprise from Pyrazolate Ligands

“…In the calculations h 1 -coordination did not constitute a minimum, and it was proposed that the presence of empty d orbitals favors h 2 -bonding over h 1 -bonding. [1] On this basis, the formation of [Ta(h 2 -Me 2 pz) 3 [18] of h 2 -Me 2 pz is 1.54, [14] whereas that of h 1 -Me 2 pz should be comparable with that of one end of a bridging Me 2 pz group (1.37). Therefore, the sum of the steric coordination numbers of the ligands in [Ta(h 2 -Me 2 pz) 5 ] (7.7) is high for an ion of the size [16] 2 ], which evidently provides the most stable steric/electronic balance (formally 16 electrons).…”

“…These are the first homoleptic pyrazolato complexes, and contain exclusively h 2 -pyrazolate ligands. This was followed by the synthesis of the homoleptic 3,5-disubstituted pyrazolatotantalum(v) complex [Ta(h 2 -Me 2 pz) 3 4 )´0.5 thf, [3] in which there is just one ligand of this type. The preparation of homoleptic pyrazolato complexes and in particular homoleptic (h 2 -pyrazolato)titanium(iv) complexes is the most significant development in the coordination chemistry of these ligands since the unexpected discovery of endo bidentate (h 2 ) coordination in [UCp 3 (h 2 -pz)].…”

“…15 %) [16] titanium(iv). [1] The failure to observe d-block transition metal complexes of h 2 -coordinated pyrazolato ligands prior to [ZrCp 2 (h 2 -pz)(thf)](BPh 4 ) [3] was attributed to a correlation between common exo bidentate binding and the directional properties of the nitrogen donor atoms. [4,6,15] Even the example of [ZrCp 2 (h d-block transition metal complexes of m-pyrazolate ligands, [6,7] can be viewed as an exceptional result of the need to achieve electronic saturation (18 electrons complexes as a general feature.…”

Synthesis, Structure, and Molecular Orbital Calculations of (Pyrazolato)vanadium(III) Complexes − Understanding η2-Pyrazolato Ligand Coordination on d2 Metal Centers

“…[7] Prior to 1997, only one example of η 2 -pyrazolato coordination to a dblock metal had been reported. [3] Since 1997, we have reported many examples of η 2 -pyrazolato ligand coordination among d 0 group-4 and -5 complexes. [4,5] Until recently, η 2 -pyrazolato ligand coordination in dblock metals was limited to systems with empty d shells.…”

Synthesis, Structure, and Molecular Orbital Calculations of (Pyrazolato)vanadium(III) Complexes − Understanding η2-Pyrazolato Ligand Coordination on d2 Metal Centers

“…[1Ϫ6] Structurally documented coordination modes in mid to late d-block metals have been restricted to η 1 -bonding to a single metal ion, [1] µ-η 1 :η 1bonding between two metal centers, [1] and our recent report of η 5 -bonding in a ruthenium complex. [3] Since 1997, we have reported many examples of η 2 -pyrazolato ligand coordination among d 0 group-4 and -5 complexes. [3] Since 1997, we have reported many examples of η 2 -pyrazolato ligand coordination among d 0 group-4 and -5 complexes.…”