| Sumari: | <p>A new family of group 4 permethylpentalene (C<small><sub>8</sub></small>Me<small><sub>6</sub></small><small><sup>2−</sup></small>; Pn*) aryloxide and alkoxide complexes have been synthesised and fully characterised by multinuclear NMR spectroscopy and single-crystal X-ray diffraction; (η<small><sup>8</sup></small>-C<small><sub>8</sub></small>Me<small><sub>6</sub></small>)Zr(OR)<small><sub>2</sub></small> (R = <small><sup><em>t</em></sup></small>Bu (<strong>1</strong>), 2,6-Me-C<small><sub>6</sub></small>H<small><sub>3</sub></small> (<strong>2</strong>), 2,6-<small><sup><em>i</em></sup></small>Pr-C<small><sub>6</sub></small>H<small><sub>3</sub></small> (<strong>3</strong>) and 4-OMe-C<small><sub>6</sub></small>H<small><sub>4</sub></small> (<strong>4</strong>)), (η<small><sup>8</sup></small>-C<small><sub>8</sub></small>Me<small><sub>6</sub></small>)Zr (OR) (R = 2,6-<small><sup><em>t</em></sup></small>Bu-C<small><sub>6</sub></small>H<small><sub>3</sub></small> (<strong>5</strong>) and 2,6-<small><sup><em>t</em></sup></small>Bu-4-Me-C<small><sub>6</sub></small>H<small><sub>2</sub></small> (<strong>6</strong>)), (η<small><sup>8</sup></small>-C<small><sub>8</sub></small>Me<small><sub>6</sub></small>)ZrCp(OR) (R = <small><sup><em>t</em></sup></small>Bu (<strong>7</strong>), 2,6-Me-C<small><sub>6</sub></small>H<small><sub>3</sub></small> (<strong>8</strong>) and 2,6-<small><sup><em>i</em></sup></small>Pr-C<small><sub>6</sub></small>H<small><sub>3</sub></small> (<strong>9</strong>)), (η<small><sup>8</sup></small>-C<small><sub>8</sub></small>Me<small><sub>6</sub></small>)TiCp(O-2,6-Me-C<small><sub>6</sub></small>H<small><sub>3</sub></small>) (<strong>10</strong>) and (η<small><sup>8</sup></small>-C<small><sub>8</sub></small>Me<small><sub>6</sub></small>)ZrCp<small><sup>Me</sup></small>(OR) (R = 2,6-Me-C<small><sub>6</sub></small>H<small><sub>3</sub></small> (<strong>11</strong>), 2,6-<small><sup><em>i</em></sup></small>Pr-C<small><sub>6</sub></small>H<small><sub>3</sub></small> (<strong>12</strong>) and 2,4-<small><sup><em>t</em></sup></small>Bu-C<small><sub>6</sub></small>H<small><sub>3</sub></small> (<strong>13</strong>)). <strong>2</strong>, <strong>3</strong>, <strong>6</strong>, <strong>7</strong>, <strong>9</strong>, <strong>10</strong> and <strong>12</strong> were studied as initiators for the ring-opening polymerisation (ROP) of <small>L</small>-lactide, and <strong>2</strong>, <strong>3</strong>, <strong>6</strong>, <strong>7</strong> and <strong>10</strong> were studied as initiators for the ROP of <em>rac</em>-lactide. <strong>3</strong> was found to be the most active initiator for the ROP of <small>L</small>-lactide (<em>k</em><small><sub>obs</sub></small> = 0.35 h<small><sup>−1</sup></small>) and <strong>2</strong> for the ROP of <em>rac</em>-lactide (<em>k</em><small><sub>obs</sub></small> = 0.21 h<small><sup>−1</sup></small>). These initiators produced isotactic PLA for the ROP of <small>L</small>-lactide and moderately heterotactic enriched (maximum <em>P</em><small><sub>r</sub></small> of 0.69) or atactic PLA for the ROP of <em>rac</em>-lactide with polymer chains consisting of polylactic acid repeat units with –OR and –OH end groups.</p>
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