Novel Platinum(IV)−Carbohydrate Complexes:  Metal Ion Coordination Behavior of Monosaccharides in Organic Solvents

New platinum(IV)-coordinated carbohydrate complexes [PtMe<sub>3</sub>L]BF<sub>4</sub> (<b>14E</b>−<b>21E</b>, <b>22D</b>−<b>24D</b>) have been prepared from the reaction of [PtMe<sub>3</sub>(Me<sub>2</sub>CO)<sub>3</sub>]BF<sub>4</sub> (<b>1</b>) with a wide range of isopropylidene-protected carbohydrates L‘ in acetone. These complexation reactions can be accompanied by a platinum-promoted cleavage of an isopropylidene group (<b>14E</b>, L‘ = 1,2;5,6-di-<i>O</i>-isopropylidene-α-d-glucofuranose (<b>1A</b>), L = 1,2-<i>O</i>-isopropylidene-α-d-glucofuranose; <b>15E</b>, L‘ = 3-<i>O</i>-acetyl-1,2;5,6-di-<i>O</i>-isopropylidene-α-d-glucofuranose (<b>2A</b>), L = 3-<i>O</i>-acetyl-1,2-<i>O</i>-isopropylidene-α-d-glucofuranose; <b>16E</b>, L‘ = 3-<i>O</i>-(methylsulfonyl)-1,2;5,6-di-<i>O</i>-isopropylidene-α-d-glucofuranose (<b>3A</b>), L = 3-<i>O</i>-(methylsulfonyl)-1,2-<i>O</i>-isopropylidene-α-d-glucofuranose; <b>17E</b>, L‘ = 1,2;5,6-di-<i>O</i>-isopropylidene-α-d-allofuranose (<b>4A</b>), L = 1,2-<i>O</i>-isopropylidene-α-d-allofuranose; <b>18E</b>, L‘ = 2,3;4,6-di-<i>O-</i>isopropylidene-2-keto-l-gulonic acid (<b>5A</b>), L = 2,3-<i>O-</i>isopropylidene-2-keto-l-gulonic acid; <b>19E</b>, L‘ = 2,3;4,6-di-<i>O</i>-isopropylidene-α-l-sorbofuranose (<b>6A</b>), L = 2,3-<i>O</i>-isopropylidene-α-l-sorbofuranose). In some cases, complexation proceeds without the loss of an isopropylidene group (<b>14E</b>, L = L‘ = 1,2-<i>O</i>-isopropylidene-α-d-glucofuranose (<b>10B</b>); <b>15E</b>, L = L‘ = 3-<i>O</i>-acetyl-1,2-<i>O</i>-isopropylidene-α-d-glucofuranose (<b>11B</b>); <b>20E</b>, L = L‘ = 1,2-<i>O</i>-isopropylidene-α-d-xylofuranose (<b>12B</b>), <b>21E</b>, L = L‘ = 5,6-<i>O</i>-isopropylidene-d-gulono-γ-lactone (<b>13B</b>)). Furthermore, complexes <b>22D</b>−<b>24D</b> with diprotected carbohydrate ligands undergo a platinum-promoted cleavage of an isopropylidene group in wet methylene chloride to give <b>19E</b>, cleavage of the carbohydrate ligand L (<b>7A</b>) to give [PtMe<sub>3</sub>(H<sub>2</sub>O)<sub>3</sub>]BF<sub>4</sub>, and substitution of the isopropylidene ligand by an aqua ligand to give [PtMe<sub>3</sub>L(H<sub>2</sub>O)]BF<sub>4</sub> (<b>24D</b>‘, L = 2,3;4,5-di-<i>O</i>-isopropylidene-β-d-fructopyranose), respectively. Complex <b>14E</b> reacted in acetone within 1 week in a platinum-promoted addition of an isopropylidene protecting group, yielding [PtMe<sub>3</sub>L‘]BF<sub>4</sub> (<b>25D</b>, L‘ = 1,2;5,6-di-<i>O</i>-isopropylidene-α-d-glucofuranose). The results show that carbohydrates can act as tridentate neutral ligands with a wide variety of donor sites:  3 × OH (<b>14E</b>, <b>17E</b>−<b>19E</b>), 2 × OH + O<sub>COMe</sub> (<b>15E</b>), 2 × OH + O<sub>SO</sub><sub><sub>2</sub></sub><sub>Me</sub> (<b>16E</b>), 2 × OH + O<sub>ring</sub> (<b>20E</b>), 2 × OH + O<sub>acetal</sub> (<b>21E</b>), 1 × OH + O<sub>ring</sub> + O<sub>acetal</sub> (<b>22D </b>-<b> 25D</b>). Bidentate ligation (OH + O<sub>ring</sub>) is observed in <b>24D</b>‘. Complexes <b>14E</b> singly <sup>13</sup>C-labeled at each of the saccharide carbons were prepared, and an analysis of the <i>J</i> couplings involving the labeled carbons permitted an assignment of the solution conformation of the carbohydrate ligand. X-ray structure analysis of <b>19E</b> (monoclinic, <i>P</i>2<sub>1</sub>, <i>a </i>= 8.607(3) Å, <i>b </i>= 9.955(4) Å, <i>c </i>= 11.415(4) Å, <i>Z </i>= 2) and <b>24D</b>‘ (orthorhombic, <i>P</i>2<sub>1</sub>2<sub>1</sub>2<sub>1</sub>, <i>a </i>= 9.851(2) Å, <i>b </i>= 11.141(4) Å, <i>c </i>= 20.418(6) Å, <i>Z </i>= 4) exhibits the same coordination in the solid state as in solution, namely, via the three hydroxyl groups, yielding a strained-cyclic system (<b>19E</b>) and a five-membered 1,3,2-dioxaplatina ring (<b>24D</b>‘).