“…The chemical shift pattern of the tether chain follows the same trend as [Pd 2 (egta)Cl 2 ] 2- . , The CH 2 nearest the coordinating N shifts upfield upon coordination. The observed Δδ value of +0.35 for this position is similar to the +0.25 value for [Pd 2 (egta)Cl 2 ] 2- .…”
Light yellow crystals of [MV][Pt(2)(hdta)Cl(2)].4H(2)O (1) (MV(2+) = 1,1'-dimethyl-4,4'-bipyridinium, hdta(4)(-) = 1,6-hexanediamine-N,N,N',N'-tetraacetate) were examined by X-ray diffraction. A 0.08 x 0.24 x 0.24 nm crystal was shown to have space group C2/c, having unit cell dimensions of a = 22.757(5) Å, b = 13.566(3) Å, and c = 12.120(2) Å and unit cell angles of alpha = gamma = 90 degrees and beta = 109.07(3) degrees with Z = 4. A total of 3195 independent reflections were refined to R = 0.0454. Each Pt(II) site has the anticipated NO(2)Cl square-planar mer coordination. The Pt-N(1) distance (N(1) is the N donor of the hdta(4)(-) ligand) is 2.001(9) Å, only slightly shorter than typical Pt-N distances (2.04-2.09 Å) for sp(3) donors. The Pt-O distances to the coordinated glycinato donors in 1 are 2.012(7) and 2.000(8) Å, values very similar to those of trans-[Pt(gly)(2)] (gly = glycinate). The Pt-Cl distance of 2.310(3) Å is in the range of 2.27-2.32 Å observed for other Pt(II)-Cl(-) bonds. The bond angles are close to the ideal 90 degrees or 180 degrees value: angleN-Pt-O = 85.4(3) degrees and 83.2(4) degrees; angleN-Pt-Cl = 176.6(2) degrees. The [Pt(2)(hdta)Cl(2)](2)(-) units are packed in an end-to-end fashion such that the [Pt(II)(iminodiacetate)Cl] headgroups are overlapping. This provides square-planar to square-planar stacking of the headgroups. (1)H and (13)C NMR data are presented which show that the [Pt(2)(hdta)Cl(2)](2)(-) coordination of the solid state is maintained in solution. The coordinated glycinato arms of [Pt(2)(hdta)Cl(2)](2)(-) are equivalent, exhibiting only one AB pattern in the (1)H NMR (H(a), 4.31 ppm; H(b), 3.89 ppm; J(ab) = 16.1 Hz) and one type of coordinated carboxylate ((13)C NMR resonance at 189.7 ppm). Time-dependent (1)H and (13)C NMR spectra show that inosine first displaces only Cl(-) in [Pt(2)(hdta)Cl(2)](2)(-) in solutions up to one inosine per Pt(II) center. A higher concentration of inosines (Ino) results in the displacement of one of the glycinato arms, detectable at 175.0 ppm by (13)C NMR. The sequential nature and binding of two Ino ligands, necessarily cis in [Pt(2)(hdta)(Ino)(4)], mimics the steps necessary to allow major groove-spanning ligation of DNA in the manner of the Farrell-type binuclear platinum(II) amine complexes.
“…The chemical shift pattern of the tether chain follows the same trend as [Pd 2 (egta)Cl 2 ] 2- . , The CH 2 nearest the coordinating N shifts upfield upon coordination. The observed Δδ value of +0.35 for this position is similar to the +0.25 value for [Pd 2 (egta)Cl 2 ] 2- .…”
Light yellow crystals of [MV][Pt(2)(hdta)Cl(2)].4H(2)O (1) (MV(2+) = 1,1'-dimethyl-4,4'-bipyridinium, hdta(4)(-) = 1,6-hexanediamine-N,N,N',N'-tetraacetate) were examined by X-ray diffraction. A 0.08 x 0.24 x 0.24 nm crystal was shown to have space group C2/c, having unit cell dimensions of a = 22.757(5) Å, b = 13.566(3) Å, and c = 12.120(2) Å and unit cell angles of alpha = gamma = 90 degrees and beta = 109.07(3) degrees with Z = 4. A total of 3195 independent reflections were refined to R = 0.0454. Each Pt(II) site has the anticipated NO(2)Cl square-planar mer coordination. The Pt-N(1) distance (N(1) is the N donor of the hdta(4)(-) ligand) is 2.001(9) Å, only slightly shorter than typical Pt-N distances (2.04-2.09 Å) for sp(3) donors. The Pt-O distances to the coordinated glycinato donors in 1 are 2.012(7) and 2.000(8) Å, values very similar to those of trans-[Pt(gly)(2)] (gly = glycinate). The Pt-Cl distance of 2.310(3) Å is in the range of 2.27-2.32 Å observed for other Pt(II)-Cl(-) bonds. The bond angles are close to the ideal 90 degrees or 180 degrees value: angleN-Pt-O = 85.4(3) degrees and 83.2(4) degrees; angleN-Pt-Cl = 176.6(2) degrees. The [Pt(2)(hdta)Cl(2)](2)(-) units are packed in an end-to-end fashion such that the [Pt(II)(iminodiacetate)Cl] headgroups are overlapping. This provides square-planar to square-planar stacking of the headgroups. (1)H and (13)C NMR data are presented which show that the [Pt(2)(hdta)Cl(2)](2)(-) coordination of the solid state is maintained in solution. The coordinated glycinato arms of [Pt(2)(hdta)Cl(2)](2)(-) are equivalent, exhibiting only one AB pattern in the (1)H NMR (H(a), 4.31 ppm; H(b), 3.89 ppm; J(ab) = 16.1 Hz) and one type of coordinated carboxylate ((13)C NMR resonance at 189.7 ppm). Time-dependent (1)H and (13)C NMR spectra show that inosine first displaces only Cl(-) in [Pt(2)(hdta)Cl(2)](2)(-) in solutions up to one inosine per Pt(II) center. A higher concentration of inosines (Ino) results in the displacement of one of the glycinato arms, detectable at 175.0 ppm by (13)C NMR. The sequential nature and binding of two Ino ligands, necessarily cis in [Pt(2)(hdta)(Ino)(4)], mimics the steps necessary to allow major groove-spanning ligation of DNA in the manner of the Farrell-type binuclear platinum(II) amine complexes.
“…The amount of η 2 pyrimidine complexes at final equilibrium with N-1 coordination decreases from 98% for pym with no CH 3 groups to 43% for 4-CH 3 pym and 32% for 4,6-Me 2 pym . Therefore methyl σ donation strengthens the Ru(II)−N bond, contributing to a higher activation barrier for N-1 to η 2 migrations . Hence the effect for 2-CH 3 pz not adopting η 2 structures upon protonation follows this trend.…”
Section: Resultsmentioning
confidence: 86%
“…In none of these studies of Ru II complexes with pyrazines has there been mention of coordination of the various pyrazine ligands in any mode other than attachment at the N-1 lone pair of electrons. The η 2 attachment of ruthenium(II) polyamino polycarboxylates, particulary [Ru II (hedta)] - , has been recently established for uracils and uridines, − cytosine and cytidines, the RNA polymerase inhibitor 6-azauridine, and simple pyrimidines and methylpyrimidines. − Factors affecting the change from N-1 to η 2 -attachment are discussed in earlier publications. − Representative structures of these η 2 complexes are as shown: Pyrazine's poorer σ donation than pyrimidine, illustrated by free ligand p K a 's of 0.60 vs 1.31, contributes to poorer to N-1 coordination stability and suggests that η 2 coordination of pyrazines is a possibility. …”
[Ru(II)(hedta)(D(2)O)](-), hedta(3)(-) = N-(hydroxyethyl)ethylenediaminetriacetate, reacts with pyrazine in D(2)O at 25 degrees C to yield several isomers and
“…Ring methylation raises the p K a of the N-1 lone pair . Therefore increasing the basicity at N-1 retards the subsequent isomerism process by increasing the barrier to rearrangement and stabilizing the N-1 bound reactant …”
[RuII(hedta)(H2O)]-,
hedta3- =
N-hydroxyethylethylenediaminetriacetate, forms N-1-bound
pyrimidine complexes
via a kinetically controlled substitution at N-1 with
pyrimidine (pym), 4-methylpyrimidine (4CH3pym), and
4,6-dimethylpyrimidine (Me2pym); k = 31
M-1 s-1 for pym.
Subsequent to N-1 coordination, an intramolecular
redistribution of RuII−pyrimidine linkage isomers occurs
with the formation of η2 attachments, reaching
equilibrium
with t
1/2's of 28.8 (pym), 24
(4CH3pym), and 1 h for Me2pym.
The N-1 forms exhibit normal RuII/III waves
at
0.14 (pym), 0.10 (4CH3pym), and 0.16 V
(Me2pym) whereas the η2 forms shift to
more positive values indicative
of better π-acceptor attachments: 0.50 (pym) and 0.44 V
(4CH3pym). The ratio of isomers was determined
to
be as follows by 1H NMR and 13C NMR methods:
(pym)
η2(1,2):η2(5,6):η2(1,6):N-1
of 43:22:33:2; (4CH3pym)
η2(1,2):η2(5,6):N-1 of 10:33:57;
(Me2pym)
η2(1,2):η2(5,6):N-1 of 6:26:68.
1H NMR assignments have been made
for all the observed N-1, η2(1,2),
η2(5,6), and η2(1,6) isomers.
13C NMR shifts have been identified for
the
major isomers of pym and 4CH3pym and confirmed HH COSY
and HC COSY methods. Several important
conclusions are drawn: (1) η2 isomers of the
η2(1,2) type exhibit significant downfield shifts of
H2 of ca 1.20
ppm; (2) 13C NMR shifts of carbon centers in
η2-bound diazine rings are downfield of the free ligand
by up to
+9 ppm and not 40−80 ppm upfield as for η2-olefinic
complexes; (3) η2 protons of the
η2(5,6) type shift
significantly less upfield than those for η2-olefin
complexes (ca. 0.4−0.8 ppm vs 1.0−2.0 ppm). It was
established
that the formation of η2-bound pyrimidines of
[RuII(hedta)]- occurs concomitantly
with the dissociation of a
carboxylate donor of the hedta3- ligand.
13C NMR spectra reveal the predicted weighted
percentage of freed
carboxylates based on the isomer distribution between N-1 with all
three glycinato arms of hedta3- bound to
RuII
(13C resonance at 188 ppm) vs η2
forms with two bound glycinato groups and one free glycinato group of
hedta3-
(resonating near 174 ppm).
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