The variations with pD of 31P, 13C and lH n.m.r. chemical shifts for D2O
solution of MePO3H2 and NH2(CH2)nPO3H2
(n = 1, 2, 3) have been studied. In the aminoalkylphosphonic
acids, δp is profoundly affected by amine deprotonation.
'Cyclic' conformations in which the amine group is close to the phosphonate group are proposed, with the strength of the
amine-phosphonate interaction decreasing as n increases.
15N and 195Pt n.m.r. have been used to study the reactions in solution of cis -Pt(15NH3)2(H2O)22+ (1), cis -Pt(15NH3)2(OH)2 (2), cis -Pt(15NH3)2Cl2 (3), Pt(15NH3)3(H2O)2+ (4) and Pt(15NH3)3(OH)+ (5) with the amino acids +NH3(CH2)nCO2- (LH) [n = 1 ( glycine, glyH ); n = 2 (β- alanine , βalaH ), n = 3 (γ- aminobutyric acid, abaH )]. While glycine with (1) gives initially cis -Pt(NH3)2( glyH -O)(H2O)2+, with facile ring closure to Pt(NH3)2( gly - N,O)+, β- alanine and γ- aminobutyric acid with (1) give solutions containing a mixture of cis -Pt(NH3)2(LH-O)(H2O)2+, cis -Pt(NH3)2(LH.O)22+, and {Pt(NH3)2}2(μO,O-LH)(μ-OH)3+, which are quite stable kinetically under mildly acid conditions. Ring closure to Pt(NH3)2(L-N,O)+ becomes increasingly difficult as n increases. At 37°C and initial pH 7, (3) with glycine gives Pt(NH3)2( gly -N,O)+, but β- alanine and γ- aminobutyric acid give predominantly cis -Pt(NH3)2Cl(LH-O)+. Compound (4) with glycine gives initially Pt(NH3)3( glyH -O)2+, which then isomerizes to Pt(NH3)3( glyH -N)2+. In corresponding reactions with β- alanine and γ- aminobutyric acid, Pt(NH3)3(LH-O)2+ is stable indefinitely under mildly acid conditions. Differences in reactivity of the amino acids with (2) and (5) in alkaline solutions may be correlated with decreasing nucleophilicity of the amine group of NH2(CH2)nCO2- as n increases.
1H, 13C and 195Pt n.m.r. spectra
have been obtained for [PtMe3(μ3-Z)]4 (Z
= Cl, Br, I, OH, N3, SMe,
SPh, and SCF3). The compounds with Z = SPh and SCF3 have not previously been prepared. In
those tetramers which contain more than one 195Pt nucleus, and where
195Pt-Z-195Pt coupling is significant, 1H and 13C
spectra cannot be interpreted as first order. Values of 2JPt-Z-Pt
have been calculated from 13C spectra where Z = SMe,
SPh, OH, and N3, and upper limits
estimated for a number of other Z. When Z = SMe and
OH, long-range 195Pt-Z-Pt-13C coupling is resolved. 2J(195Pt-S-13C)
when Z = SMe and SCF3, and 3J(195Pt-S-C-19F)
when Z = SCF3, are unexpectedly small. The 195Pt
resonance frequency decreases in the order Z = OH > SPh
> SMe > N3 ≈ Cl > Br ≈ SCF3 > I. To assist in
analysing the spectra transition frequencies and intensities have been
calculated for the AA'2X spectrum (available as an accessory publication).
The complex [Co( acac )2(NO2acac)] has been isolated after fractional crystallization from a reaction mixture of [Co( acac )3] and nitrating agent. The complex crystallizes in the triclinic space group P1, with c 14.557(2) � , α 78.98(1), β 83.71(2), γ75.32(1)° and Z 2. The structure refined to a final R value of 0.074 for 2287 'observed' [I > 3 σ(I)] reflections. The structure consists of discrete complex molecules with the cobalt atom surrounded by six oxygen atoms at the corners of a distorted octahedron. The NO2 group is twisted at 50.7� to the chelate ring on which it is situated and has little influence on the geometry, with intrachelate and interchelate oxygen-oxygen separations essentially the same as those found in [Co( acac )3]. The 59Co n.m.r. spectra of the [Co( acac )2(NO2acac)] complex, as well as [Co( acac )3], [Co(NO2acac)3] and [Co( acac )(NO2acac)2], have been recorded, this resonance being particularly sensitive to substitution on they γcarbon atom of the acetylacetonato chelate ring. The 59CO relaxation rates for the [Co( acac )2(NO2acac)] and [Co( acac )(NO2acac)2] complexes are faster than that displayed by the symmetric [Co(NO2acac)3] complex, (1948 � 20, 2765 � 30 and 1696 � 20 s-1, respectively). The results obtained for the relaxation rates for these complexes are compared with those obtained for similar halide-substituted complexes [Co( acac )3-n( Xacac )n] � (X = Cl , Br, I; n = 0-3).
The 13C n.m.r. spectrum of the dimer [PtMe2Br(MeOH)(p-OH)]2, formed by dissolving the complex
[PtMe2Br(OH)]n in methanol, has been analysed, to give 2JPt-O-Pt 103.6 HZ. 1H and 1H-decoupled
195Pt spectra show complex patterns owing to superposition of spectra from different isotopomers.
By contrast, solutions of [PtMe2Br2]n in methanol, which contain monomeric PtMe2Br2(MeOH)2,
give simple spectra.
[PtMe2Br(OH)]n dissolves in dilute aqueous KOH solution at pH 9 to give a solution containing
the 'inert' dimer [PtMe2Br(OH)(μ-OH)]22-. Other species are present at higher pH, but the solution
never contains simple PtMe2Br(OH)32- alone. Dissolution of [PtMe2(OH)2(H2O)1.5]. in alkali at
pH 12 gives a dimer [PtMe2Br(OH)(μ-OH)]22- whose 13C n.m.r, spectrum has been analysed to
give 2JPt-O-Pt 123 .5 HZ.
Progressive substitution of water in fac-PtMe3(H2O)3+ by pyridine causes regular 195Pt shifts
to lower frequency. 195Pt, 13C and 1H data indicate that fac-PtMe3X32- exist as simple anions for
X = NO2, CN, but not for X = NCS.
195Pt chemical shifts of di- and tri-methylplatinum(IV) complexes are discussed. The hydroxobridged
dimers resonate at higher frequencies than monomeric complexes, owing to strain in the
four-membered Pt(OH)2Pt rings. is much more sensitive to the cis influence than 2JPt-CH3.
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