Neutral triazacyclononane-amide lanthanum dialkyl and dialkynyl complexes were synthesized and structurally characterized. A cationic triazacyclononane-amide lanthanum monoalkyl species was generated and found to be highly active (tof > 100 h-1) in the rare cis-selective catalytic linear dimerization of phenylacetylene.

A series of rare earth metal dialkyl complexes was prepared with the general formula [Me 2 TACN-(B)-NR]M(CH 2 SiMe 3 ) 2 (TACN ) 1,4,7-triazacyclononane, B ) (CH 2 ) 2 , SiMe 2 ; R ) tBu, secBu, nBu; M ) Sc, Y, Nd, La). For M ) Sc, mixed monoalkyl-monochloro complexes were also accessible. Selected examples of these complexes were structurally characterized and show the metal in a distorted octahedral environment. With Lewis or Brønsted acid activators the dialkyl compounds can be converted to the corresponding monoalkyl cations, which were characterized by NMR spectroscopy. Comparative testing in catalytic ethylene polymerization showed that the catalyst activity is most strongly influenced by the metal ionic radius, but that variations in the ligand backbone and substitution pattern do influence other factors, such as polymer molecular weight and catalyst stability. Catalysts with the intermediately sized rare earth metal yttrium generally showed the highest activity, but some of these catalysts produce polyethylene with broad molecular weight distributions, suggesting multisite behavior. Hypothetically this could be caused by intermolecular ligand scrambling processes. Evidence that these may occur was found in the isolation of the "half-flyover" bimetallic yttrium complex {[η 3 :η 1 -[Me 2 TACN(CH 2 ) 2 NtBu]Y-(CH 2 SiMe 3 )}{η 3 :µ-η 1 -[Me 2 TACN(CH 2 ) 2 NtBu]Y(CH 2 SiMe 3 ) 3 .

The copper-catalyzed Click reaction of phenyl azide with ethynylphosphine oxides provides new P-substituted triazoles. With tris(ethynyl)phosphine oxide this route affords a versatile scorpionate ligand that coordinates to RhCl 3 as a tripodal N ligand. Upon reduction, the same ligand can act as a P donor to W(CO) 5 . Both coordination modes can be combined, giving access to a bimetallic Mo/W complex.

The parent tris(pyrazolyl)phosphine and its 3,5-Me2, 3-Ph, and 3-t-Bu derivatives have been prepared by a simple procedure and show modest Lewis basicity of the phosphorus apex as was established by the magnitude of the (1)JP,Se coupling constant of the phosphine selenides. Because of the chelating properties of both the N- and P-sites, neutral phosphorus-centered scorpion ligands allow coordination modes that are unavailable to the abundantly used anionic tris(pyrazolyl)borate scorpionates as we established for Cu(I)-complexation. The substituted P-scorpion ligands only allow for N-coordination, as the P-apex is presumably less accessible. Two X-ray crystal structures were obtained for the Cu-complex of tris(3,5-dimethylpyrazolyl)-phosphine with acetonitrile and triphenylphosphine in the fourth coordination site. The parent P-scorpion ligand can chelate with both its pyrazolyl groups and its P-apex with the product depending on the ratio in which it is mixed with the Cu(I) complex. Reacting two equivalents of the ligand with [Cu(MeCN)4][PF6] resulted in a complex in which Cu is coordinated to the three pyrazolyl groups of one ligand and to the P-apex of the other ligand as confirmed by an X-ray crystal structure determination and a DFT computational analysis. Reacting the ligand and the Cu(I) complex in an equimolar ratio resulted in a remarkable one-dimensional P-scorpion coordination polymer for which a single crystal X-ray structure could be determined. A detailed analysis of the structural features is presented.

A set of substituted tris(pyrazolyl)phosphine oxides (OP(pz x ) 3 ) has been prepared in high yield and applied as neutral scorpion-type ligands. The P apex provides a convenient spectroscopic handle. Substitution at the 3-position of the pyrazolyl ring influences the steric demands of the ligand, while substitution at the 5-position enhances the stability. Copper(I) acetonitrile complexes of the OP(pz x ) 3 ligands were prepared and tested in ligand exchange reactions with PPh 3 and CO. The ν(CO) values of the carbonyl complexes demonstrate the electron-withdrawing properties of the ligands. These observations show that OP(pz x ) 3 ligands are an interesting extension of the widely used scorpion-type ligands.

Keywords: Tridentate ligands / Tripodal ligands / Transition metals / Copper / Density functional calculationsDFT calculations were performed on copper(I) complexes of neutral scorpion ligands based on either pyrazolyl (Pz) or triazolyl (Tz) rings with both methane and phosphine oxide apices, that is, HC(Pz) 3 , OP(Pz) 3 , HC(Tz) 3 , and OP(Tz) 3 . The analyses reveal that all four ligands have similar donor properties and that their differences are easily compensated by the proper choice of substituents. This computational study [ ‡] These authors contributed to the generation of crystals of [E Ph Cu] 2 [BArF 24 ] 2 suitable for X-ray crystal structure determination.

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The anionic tris(pyrazolyl)borates, or scorpionates, have proven to be extremely useful ligands. Neutral tris(pyrazolyl)methane ligands, however, are difficult to prepare and require numerous purification steps for a number of substitution patterns. We have previously outlined two different routes for accessing neutral tris(pyrazolyl) ligands. We describe here an adaptation of the previously published procedures for the synthesis of the electron-poor ligand tris(3,4,5-tribromopyrazol-1-yl)phosphine oxide, CBrNOP. Similar electron-deficient ligands have been proven to unlock unique chemistry for the anionic scorpionates. The title perbrominated tris(pyrazolyl)phosphine oxide displays a network of halogen bonds in the solid state. All the bonds in the pyrazole ring are rather similar to the reported borate analogues, which makes this molecule promising as a ligand for applications where very electron-poor metal complexes are required.