China is buying the dollar equivalent of $50 billion, or roughly 10 percent, of the IMF's first bond sale. The IMF is raising the cash in order to lend to developing and emerging market economies. The Europeans say they will contribute 125 billion euros, about a third of the goal. Brazil and Russia have expressed interest in the sale. To the extent that the IMF is helpful (a debatable point), these are good things. But the sign of a smart policy is that those who do good are also in a position to profit from it.
In addition to improving China's status in the IMF, the interesting point is the purchase is in Yuan (341.2 billion), a currency not traded on global markets, rather than dollars. This fits with a general policy of spreading the yuan. China already has a currency swap deal with Argentina, and has negotiated lending yuan to the central Banks of Malaysia, South Korea, Indonesia, and Belarus in the event of an emergency. While the IMF bonds are denominated as Special Drawing Rights (SDR) the IMF may lend yuan to developing countries, who could start using the yuan as a reserve currency. This encourages the transition from the dollar to SDRs, and a swap of dollars for yuan.
This isn't some sinister conspiracy. It's just good sense, if China has doubts about the dollar.