A new NON-donor ligand, 4,5-bis(2,6-diisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylxanthene (H 2 -[XA 2 ], 1), was prepared by palladium-catalyzed coupling of 2,6-diisopropylaniline with the appropriate dibromoxanthene precursor. Stable K 2 (dme) 2 [XA 2 ] (2) and Na 2 [XA 2 ] (3) salts were accessible by deprotonation of H 2 [XA 2 ] with KH in dme or NaH in toluene. The thermally unstable lithium salt of McConville's 2,6-bis(2,6-diisopropylanilidomethyl)pyridine ligand (Li 2 [BDPP], 4) was isolated by deprotonation with nBuLi or LiCH 2 SiMe 3 in hexanes at low temperature. Reaction of [ThCl 4 (dme) 2 ] with Li 2 [BDPP] or M 2 (dme) n [XA 2 ] resulted in the formation of pentagonal bipyramidal [LThCl 2 (dme)] complexes (L ) BDPP, 5; XA 2 , 6). Subsequent reaction of 5 or 6 with LiCH 2 SiMe 3 gave base-and salt-free dialkyl complexes, [LTh(CH 2 SiMe 3 ) 2 ] (L ) BDPP, 7; XA 2 , 8), which are stable for days in solution at 90 and 70°C, respectively. Complexes 5, 7, and 8 were also accessible by initial combination of 2 or 4 equiv of LiCH 2 SiMe 3 with [ThCl 4 (dme) 2 ], followed by addition of H 2 L. These reactions likely proceed by alkane elimination, but dialkyl or tetraalkyl thorium intermediates were not identified. The X-ray crystal structure of 8 suggests the presence of R-agostic C-H-Th interactions for both alkyl groups. In solution, 7 and 8 exhibit temperature-dependent 1 J C,H coupling constants for ThCH 2 , demonstrating the presence of R-agostic interactions which become increasingly favored at lower temperature. Reaction of 5 with Li 2 [BDPP] at 0°C or 7 with H 2 [BDPP] at 100°C resulted in the formation of extremely sterically encumbered [Th(BDPP) 2 ] (9), which adopts a highly distorted six-coordinate geometry with the four anilido groups arranged in an approximate tetrahedron around thorium. Bisligand complexes were not accessible with the XA 2 platform, presumably due to increased ligand rigidity.

Reaction of the neutral dialkyl complex [(XA2)Th(CH2SiMe3)2] {1; XA2 = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene} with [CPh3][B(C6F5)4] in benzene or toluene at room temperature resulted in the formation of [(XA2)Th(CH2SiMe3)(η6-arene)][B(C6F5)4] {arene = C6H6 (5) and toluene (5B)}, which were characterized by 1H, 13C, and 2D NMR spectroscopy and by X-ray crystallography (for 5). In close analogy, reaction of [(XA2)Th(CH2Ph)2] (3) with [CPh3][B(C6F5)4] in toluene at room temperature resulted in the formation of 1 equiv of Ph3CCH2R (R = Ph) and precipitation of an insoluble orange-brown oil, which upon layering with hexanes yielded crystals of [(XA2)Th(η2-CH2Ph)(η6-C6H5Me)][B(C6F5)4] (6). NMR investigation of the reactions of 1 and 3 with substoichiometric amounts of [CPh3][B(C6F5)4] provided no evidence for dinuclear monocation formation. By contrast, reaction of [(BDPP)Th(CH2Ph)2] {4; BDPP = 2,6-bis(2,6-diisopropylanilidomethyl)pyridine} with 0.5 equiv of [CPh3][B(C6F5)4] resulted in the precipitation of an insoluble oil containing a mixture of a mononuclear and a dinuclear cation; the dinuclear cation was identified as [(BDPP)Th(η2-CH2Ph)(μ-η1:η6-CH2Ph)Th(η1-CH2Ph)(BDPP)][B(C6F5)4] (7) by X-ray crystallography. Reaction of complex 3 with B(C6F5)3 resulted in the formation of [(XA2)Th(η1-CH2Ph)][η6-PhCH2B(C6F5)3] (9), which was characterized in solution by NMR spectroscopy. Complexes 5, 5B, and 6 are rare examples of arene solvent-separated ion pairs, complex 9 exists as a tight contact ion pair, and dinuclear 7 exhibits a unique benzyl ligand bridging mode. The structures of cations 5−7 and 9 highlight a pronounced tendency for these systems to engage in arene π-coordination.

Reaction of [(XA2)ThCl2(dme)] [XA2 = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene] with 2 equiv of PhCH2MgCl resulted in the formation of solvent-free [(XA2)Th(CH2Ph)2] (1). Subsequent reaction of 1 with either 1 or 2 equiv of B(C6F5)3 allowed isolation of the first non-cyclopentadienyl actinide alkyl cation, [(XA2)Th(CH2Ph)][PhCH2B(C6F5)3] (2), and a rare example of an actinide dication, [(XA2)Th][PhCH2B(C6F5)3]2 (3). The X-ray crystal structure of the dication reveals π-coordination of both PhCH2B(C6F5)3 anions, and solution NMR spectroscopy shows that a similar mode of contact ion pairing is operative in the monocation.

Two a-amino acids, 3-phosphono-2-aminopropionic and 4-phosphono-2-aminobutyric, are used to link zinc atoms in three-dimensional structures where the three phosphonic and one of the carboxylic oxygen atoms coordinate to the metal, while the protonated amino groups and the second carboxylic oxygen atom are not coordinated and remain terminal in the voids of the framework.

Upon contact with ethylene, the Phillips Cr/silica catalyst must selfalkylate before polymerization can begin. How this happens has been a mystery for over 60 years, being not only of scientific interest but also of commercial importance. Consequently, many controversial schemes have been proposed, including some that hold the initial PE chain to be different from all subsequent chains, starting with a vinyl group, instead of the usual methyl group. In this study, polymer chains produced by the Cr(II)/silica−titania catalyst at low yield were analyzed in an effort to identify the starting group on the first chain produced. The PE/Cr yield was deliberately kept low to avoid diluting that initial chain with other chains produced afterward. The polymer was then characterized by gel permeation chromatography and 13 C NMR (natural abundance). Strong signals from methyl end groups were present, but terminal vinyl groups were not detected. Likewise, analysis by proton ( 1 H) NMR also indicated a general lack of vinyl chain ends. An attempt was also made to identify the first species on the initial chain through isotopic labeling. Deutero-ethylene (C 2 D 4 ), deutero-propylene (C 3 D 6 ), or 13 Cethylene was first "preadsorbed" onto the divalent catalyst at −78 °C, where polymerization does not occur. After evacuating the excess isotopically labeled monomer, polymerization was conducted with unlabeled ethylene (C 2 H 4 ) at higher temperatures. Deuterium ( 2 H) NMR analysis of the polymers again indicated a strong methyl signal but no resonance from deuteriumcontaining vinyl chain ends. Comparison of the different NMR methods indicated a high degree of deuterium enrichment in the methyl chain ends. These results indicate that the initial chain in these experiments began with a methyl group, not a vinyl group as has sometimes been contemplated. Although helpful, this information still leaves the mechanism of site alkylation unclear because there is not enough hydrogen in ethylene to produce a methyl-initiated chain, without some other (still undefined) reaction also being involved to furnish the additional hydrogen, such as the creation of a permanent ligand.