Chelation and Stereodynamic Equilibria in Neutral Hypercoordinate Organosilicon Complexes of 1-Hydroxy-2-pyridinone

Abstract

A series of neutral organosilicon compounds, R3Si(OPO) [R = Me (1), Et (2), Ph (3)], cis-R2Si(OPO)2 [R = Me (4), Et (5), iPr (6), tBu (7), Ph (9)], (CH2)3Si(OPO)2 (8), and cis-R2Si(OPO)Cl [R = Me (10), Et (11)] (OPO = 1-oxo-2-pyridinone) have been prepared and fully characterized. X-ray crystallographic analyses show 1 to be tetracoordinate, 3, 7, and 10 to be pentacoordinate, and 4, 5, 6, 8, and 9 to be hexacoordinate. In the hexacoordinate structures, a mixture of diastereomers is observed in the form of C/N site disorder in each OPO ligand. Variable-temperature 13C and 29Si NMR studies indicate reversible Si←OC bond dissociation occurring in all pentacoordinate and hexacoordinate complexes to a varying degree with greater tendency toward dissociation in hydrogen-bonding donor solvents. Significant weakening of the dative Si←OC bond in 3 is observed in the co-crystallized adduct solvate, 3•Ph3SiOH•½C5H12, providing structural evidence for the decrease in coordination number of the OPO ligand by hydrogen-bonding donors. In the hexacoordinate complexes, increasing steric bulk of ancillary ligands also was found to promote dissociation. 1H and 13C VT-NMR studies of 4, 6, 8, and 9 indicate stereoisomerization equilibria concurrent with Si←OC bond dissociation proposed to occur through trigonal bipyramidal intermediates.

A 3,2-Hydroxypyridinone-based Decorporation Agent that Removes Uranium from Bones In Vivo

“…These come as a result of the change in coordination numbers between UO 2 -5LIO-1-Cm-3,2-HOPO (4.7 ± 0.6) and UO 2 (NO 3 ) 2 (5.6 ± 0.6). The calculated bond distances of UO 2 -5LIO-1-Cm-3,2-HOPO are in good agreement with the structural data reported of the uranyl hydroxypyridinone compounds 25,32,33 .…”

(2-Pyridyloxy)silanes as Ligands in Transition Metal Coordination Chemistry

“…In both of the compounds, the Si atom is essentially tetracoordinate and the coordination sphere may be described as (4 + 3) in MeSi(pyO) 3 and (4 + 4) in Si(pyO) 4 , because of the pyridine N atoms, which are capping the faces of the tetrahedral coordination spheres from distances close to the sum of the van-der-Waals radii (ranging between 2.91 and 3.03 Å). This tetracoordination of Si in Si(pyO) 4 is in contrast to the Si hexacoordination in the thio analog Si(pyS) 4 [27] (and other pyS-bearing Si compounds [28]), in which two of the 2-mercaptopyridyl ligands form four-membered chelates, and in complexes of the N-oxide of the pyO system, which forms five-membered chelates [29,30]. (1), O1-Si1-O2 114.68 (5), O2-Si1-O3 112.74 (5), O1-Si1-O3 97.77 (5), O1-Si1-C16 111.96 (7), O2-Si1-C16 106.…”

Crystal structures of tris[1-oxopyridine-2-olato(1−)]silicon(IV) chloride chloroform-d1disolvate, tris[1-oxopyridine-2-olato(1−)]silicon(IV) chloride acetonitrile unquantified solvate, andfac-tris[1-oxopyridine-2-thiolato(1−)]silicon(IV) chloride chloroform-d1disolvate

“…The dihedral angles formed between the O 2 Si chelate and OPO ligands are also similar to those of QOXSIF (9.39, 3.08, and 2.41 ). Structures of monodentate organosilicon OPO complexes include Ph 3 Si(OPO)ÁPh 3 Si(OH)Á0.5n-pentane, Me 3 Si(OPO), and tBu 2 Si( 1 -OPO)( 2 -OPO) (respective CSD refcodes NITRIT, NITROZ, and NITSOA; Kraft & Brennessel, 2014), and of bidentate organosilicon OPO complexes include Ph 2 Si(OPO) 2 , Me 2 Si(OPO)Cl, Ph 3 Si(OPO), Me 2 Si(OPO) 2 , Et 2 Si(OPO) 2 , iPr 2 Si(OPO) 2 , tBu 2 Si( 1 -OPO)( 2 -OPO), and (CH 2 ) 3 Si(OPO) 2 (respective CSD refcodes NISMIN, NISMOT, NITRUF, NITSAM, NITSEQ, NITSOA, NITSIU, and NITSUG;Kraft & Brennessel, 2014), and [Si(OPO) 2 (-CH 2 CH 2 SCH 2 C( O)O)] 2 Á2CH 3 CN and [O(CH 2 ) 3 ]Si(OPO) 2 (respective CSD refcodes UBUWET and UBUWIX; Tacke, Burschka et al, 2001). (I) and (II) have 0.06-0.17 Å shorter Si-O bond lengths and 3-5 larger ligand bite angles than those in chelated R 2 Si(OPO) 2 (R = alkyl, phenyl) complexes, indicating a stronger chelate presumably due, in part, to their cationic character.…”

“…[Si(OPO) 3 ]ClÁ2CDCl 3 (I): (CH 2 ) 3 Si(OPO) 2 was prepared according to the literature method (Kraft & Brennessel, 2014). (CH 2 ) 3 Si(OPO) 2 was heated in an oil bath at 463 K for 3 days in CDCl 3 upon which crystals of (I) deposited.…”