Johannes H. Groen

INSERTION REACTIONS INTO PALLADIUM-CARBON BONDS OF COMPLEXES CONTAINING NEW RIGID BIDENTATE NITROGEN LIGANDS

Abstract The neutral complexes Pd(Me)Cl(DPIA) (3) and Pd(Me)Cl(DQIA) (4), containing the novel rigid bidentate nitrogen ligands (5,6-dihydro-[1]pyrindin-7-ylidene)-isopropylamine (DPIA) and (6,7-dihydro-5H-quinolin-8-ylidene)-isopropylamine (DQIA), respectively, have been synthesized. Complexes 3 and 4 react quantitatively with CO to give the neutral acylpalladium complexes Pd(C(O)Me)Cl(DPIA) (6) and Pd(C(O)Me)Cl(DQIA) (7), respectively. Complexes 3, 4, 6, and 7, which were present as mixtures of the cis and trans isomers, were fully characterized, and in the case of complexes 6 and 7 single crystal X-ray structures have been determined. The molecular structure of 6 and 7 show a square planar geometry with the α-diimine ligands coordinated in a bidentate fashion with comparable bite angles of about 78°. The acylpalladium complexes 6, 7, and Pd(C(O)Me)Cl(iPr–PyCa) (5), containing the nitrogen ligand 2-(N-2-propanecarbaldimino)pyridine (iPr–PyCa), which is the flexible analogue of DPIA and DQIA, react with norbornadiene to yield the ionic alkyl complexes [Pd(C7H8C(O)Me)(DPIA)]Cl (9a), [Pd(C7H8C(O)Me)(DQIA)]Cl (10a), and [Pd(C7H8C(O)Me)(iPr–PyCa)]Cl (8a), respectively. Interestingly, the nature of the α-diimine ligand influences the reaction rate of the norbornadiene insertion in the order N–N=DQIA≪iPr–PyCa

Absorption of iron compounds from the small intestine in the rat

Abstract The absorption of different iron salts was studied after they had been introduced into a closed loop of small intestine in the anaesthetised rat. The absorption of iron from solutions of various salts (ferrous, ferric or complexes) in these loops was so small that it could not be demonstrated. A definite absorption was found when to the iron salts were added either an organic reducing agent (ascorbic acid, cystein, glutathione, formaldehyde sulphoxylate) or some organic acid. Especially plant acids (citric, tartaric, succinic, malic acid), lactic acid, pyruvic acid and some amino acids (glutamic, aspartic acid) were active in this respect. It appeared that the absorption under these circumstances proceeded only so long as the p H inside the intestine remained acid. The addition of hydrochloric or phosphoric acid did not promote the absorption. The author presents the following explanation for these findings: 1. 1. Iron is absorbed as ferrous ion only. 2. 2. Iron can persist in the ionised ferrous form only in acid medium. 3. 3. The normal p H of the small intestine is about 6. At this p H , almost aH the iron is transformed in the complex or ferric form, neither of which is absorbed to a measurable degree. This explains the poor absorption of iron from a simple solution introduced into the gut. 4. 4. The intestine tends to reestablish its neutral reaction if acids are introduced together with the iron salt. Hydrochloric and phosphoric acid are very quickly absorbed. For this reason these acids cannot keep the p H inside the gut down for a long time and therefore do not promote iron absorption to a measurable degree. 5. 5. The organic acids and reducing agents (all acid in character) that promote iron absorption, appear to do so by keeping the p H of the intestine down for a longer time. As soon as the intestinal content becomes neutral, all the iron is transformed into the complex or ferric form and the absorption stops. The importance of these facts for the understanding of the mechanism by which iron is absorbed, for the choice of the best preparation for iron therapy and for the elucidation of the problem of iron availability is discussed.

Synthesis, characterization and reactivity of ionic palladium(II) complexes containing bidentate nitrogen ligands in a unidentate coordination mode,

Abstract The novel ionic complexes [Pd(Me)(p-An-BIAN)(LL)]SO3CF3 (LL=p-An-BIAN (bis(anisylimino)acenaphthene) (1a), phen (2a), dmphen (3a), dppe (4a), dppp (5a)) have been synthesized via the reaction of [Pd(Me)(NCMe)(p-An-BIAN)]SO3CF3 with LL. The X-ray crystal structure of complex 1a has been determined and shows a distorted square planar geometry in which one BIAN ligand is coordinated in a bidentate fashion (PdN(1)=2.037(4) A; PdN(2)=2.189(4) A) and, interestingly, the other BIAN ligand in a unidentate fashion (PdN(3)=2.066(4) A; PdN(4)=2.714(6) A). Spectroscopic data of the mixed ligand complexes [Pd(Me)(p-An-BIAN)(LL)]SO3CF3 (LL=phen (2a), dppe (4a), dppp (5a)) indicate that the LL ligand is coordinated in a bidentate fashion and the p-An-BIAN ligand in a unidentate fashion, which is in agreement with the larger complexation strength of the phen, dppe and dppp ligands, as compared with that of the p-An-BIAN ligand. In contrast, complex 3a (LL=dmphen) contains a bidentate p-An-BIAN ligand and a unidentate dmphen ligand, which can be explained by the sterically demanding methyl groups of the dmphen ligand. Complexes 1a–4a underwent insertion of carbon monoxide, resulting in the formation of acetylpalladium complexes [Pd(C(O)Me)(p-An-BIAN)(LL)]SO3CF3 (1b–4b). Since mass-law retardation by excess p-An-BIAN has been observed for CO insertion for complexes 1a and 4a, it is proposed that the mechanism involves dissociation of the unidentate nitrogen ligand. Complexes 1a–5a and 1b–4b show fluxional behavior due to flipping of the unidentate nitrogen ligand. Complexes 1a–3a and 1b–3b also show fluxional behavior due to site exchange of the nitrogen atoms of the bidentate nitrogen ligand. A mechanism for this exchange process has been proposed. This mechanism involves (a) substitution of a nitrogen atom of the bidentate nitrogen ligand by the uncoordinated nitrogen atom of the unidentate nitrogen ligand, (b) flipping of the unidentate nitrogen ligand, and (c) a second nitrogen substitution reaction. Reaction of the acetylpalladium complexes 1b–4b with norbornadiene led to dissociation of the unidentate nitrogen ligand and formation of the known alkylpalladium complexes [Pd(C7H8C(O)Me)(p-An-BIAN)]SO3CF3 (1c), [Pd(C7H8C(O)Me)(phen)]SO3CF3 (2c), 1c, and [Pd(C7H8C(O)Me)(dppe)]SO3CF3 (4c), respectively.